The ratios are in the table at the bottom of this article from Building Science Corp. https://buildingscience.com/documents/building-science-insights-newsletters/bsi-100-hybrid-assemblies

You have to have a certain ratio of interior and exterior insulation in order to keep the sheathing above the dew point. The more insulation you stuff in the cavities, the more continuous insulation you have to add to the outside to compensate for the reduction in heat energy making it to the sheathing. There are tables in the IRC that should help. You can also use your search engine of choice to search for wall insulation ratios for your climate zone. https://codes.iccsafe.org/content/IRC2018/chapter-11-re-energy-efficiency

Venting roofs doesn’t really make them cooler. The shingles and sheathing are going to be roughly the same temperature vented or not, and that heat is going to radiate into the space. You might experience a sensation of coolness from the air movement on your sweaty skin, which will bring some relief. A radiant barrier below your rafters would likely do more than venting will to make it feel cooler. If you have a window, open that along with the garage door to get a cross breeze when you’re in there.

I believe what you have is a welded steel door frame with integral hinges. This might help you out: https://www.doityourself.com/forum/hardware-fasteners/583281-replacement-hinges-welded-steel-door-frame.html

Don’t even need to approximate. Hold a scrap or your rail cut to rough length on the top of the skirt board and against the post and wall. Mark the angles using the wall and post as the straight edges. If everything’s plumb, you’ll cut both at the same angle.

I kind of doubt it’s pine; the long little speckles suggest and open-grain hardwood, though the stain makes it hard to determine the species. I’d suspect oak or ash, though the grain doesn’t quite look right for either. If it were pine, I’d expect to see some gouging or dents in a pine table, since pine is so soft. And even with wood conditioner, pine is really difficult to stain, especially dark colors. This would be about the best stain job on pine I’ve ever seen. I’ve done a little experimentation with undercoats/pore sealers for staining blotch-prone woods, and I’ve found wipe-on polyurethane to be the best. Two thin coats of that work reasonably well under gel stain on pine - better than wood conditioner, varnish, and other types of polyurethane. It might work for you here as well, though you’ll still want to at least scuff sand the surface with 320 grit or higher for the poly to bond.

A hammer and a big flat bar or something similar should work. Even a big flat shovel or floor scraper - whatever you have that you can hammer into the joint between the wall and the stud. Start at an end - top or bottom - and work to the other end. If the nails pull through the studs, no big deal. You can use vise grip pliers to kind of twist the nails back and forth until they loosen, or if you don’t have those, just tap the exposed nail back and forth with a hammer until they fall out or break off.

Personally, I’d take the framing (really furring) out first. Make sure there are no leaks in the wall or walls, and if there are you have to fix those before you think about insulating. For insulation, rigid foam right against the foundation to cut off thermal bridging. Foam thickness depends on climate zone and insulation type (eps, xps, polyiso, phenolic). Then reinstall the furring and fasten your drywall to that.

2x3 exterior wall framing? Is this infill in a timber frame, pole barn, or something similar? Knowing what kind of structure this is would be helpful in recommending an insulation strategy.

A prehung door comes “prehung” in a frame. You’d have to either pull out the existing frame to put in the prehung door, or - I’ve never seen it done but it could be possible - leave the existing frame and buying a prehung door sized to fit inside that frame, similar to what’s done with a replacement window. You’d lose width and height, and you’d probably end up spending a bunch extra to get a custom-size door (it would probably be about 78 in. tall, and about 2 in. narrower than your existing door). You could also cut down an off-the-shelf prehung door and frame to fit the space, but then you’re getting into territory similar to installing a slab. Like I said, I’ve never seen anyone do this - never seen anyone want to shrink their doors - but there’s not really a reason it can’t be done.

You have a couple prescriptive options available in the model code if you go the path of insulating the walls, which is a good choice. Look at R408.3 in the International Residential Code - it spells it out pretty clearly. For a more plain-language perspective explanation, I’d check out the Fine Homebuilding article “crawlspaces that work.” Code available here: https://codes.iccsafe.org/content/IRC2021P1/chapter-4-foundations

Why does the inspector say this must lock open? It can’t be an emergency escape and rescue opening (commonly referred to as egress window), as it’s too high off the ground and not tall enough. Just curious what specific code issue he’s concerned about. Also, did the window open before tue ceiling was drywalled? If so, you might want to talk to whoever finished the basement, not the original builder. Also, if they used 1/4-in. drywall on your ceiling as you say, that’s highly unusual.

I wish people would stop saying attics or buildings need to breathe - it’s just not true. People need to breathe; building assemblies made of materials that can rot need to stay dry. One way to keep them dry is to give them space to dry into, and that is often achieved by venting. However, all vents need to be outboard of insulation (on the side that’s cold in winter). Any insulation on the outside of a vent is doing as much good for a house as it would do sitting on a rack at the lumber yard.

Attic vents are not for cooling; they are for venting moisture out of an attic space. Venting has roughly zero effect on the temperature inside an attic or on the temperature of a roof deck.

Old-timers (people who were around when insulation started to become common in the 1900s) came up with the notion that houses needed to breathe when paint started to fall off of the siding on walls that had recently been insulated. The issue was vapor pressure, not inability to breathe, but folks back then didn’t know any better. There’s been about a century of research on building science since then. Anyone interested in the topic can look at the decades of research done by Building Science Corp., or for a crash course, check out the recently published book, “Houses need to breathe - or do they?” Spoiler alert: I gave it away up top. (Edited to consolidate two comments in one for clarity)

What do you mean by “4x4 post bracket”?typical post bases handle lateral displacement - prevent the bottom of the post from getting kicked out - not hold posts upright. There is special hardware that you can bury in concrete to do that - it’s called a moment post base. The ones I’m familiar with, the concrete gets poured around it; it isn’t something you can bolt to a footing afterwards. And they’re at least $150/each for a 4x4 version, just for the hardware. Can’t remember height limit off the top of my head, but fence heights are often limited by code, and model code max I believe is 7ft. https://www.strongtie.com/standoffpostbases_castinplacepostbases/mpb_base/p/mpbz#ProductDetails

For a fence? The only restriction on fences I’m aware of in the model code (IRC) is height. Jurisdictions often put restrictions on fence setbacks and modify the IRC height, but a restriction on galvanized fence posts being set in concrete?