If you can find an oil/solvent based sealer in your area, that would make the sealing, sanding, sealing part the smoothest.

If you are doing it with a water borne finish, then you want to use a high solids content sanding sealer.

If you want smooth, not sure why you are rolling it instead of spraying it.

I was just concerned about the aerosols in my basement as its not too well ventilated, plus I didn't want to get air bubbles. Usually im better at painting by rolling compared to spray. Additionally more color options if I didn't use spray paint.

Any idea as to what kind of paint I could use for the primer and actual color paint if im rolling?

More color options? You can spray any paint that can be rolled.

I would go to an actual paint store (not a big box hardware store) for your paint. For durability, buy the best you can afford and (generally) the greater the sheen (gloss) the greater the durability. Have the store tint the primer.

And finally, cover the final paint with a high quality clear coat (this will add durability, less likely to show scratches than paint, and then you can also adjust the sheen to what you want regardless of the paint's sheen)

I had good success just using cheap paint from the dollar store for a MDF halloween project.

I built a desk with MDF and used BIN Primer/sealer on it. 3 coats with fine sanding in between, rolled on with a low pile roller. MDF soaks up the sealer and you end up with a smooth, hard surface. Try it on a piece of scrap MDF first to get an idea of what the final result will be.

A non-waterbased primer would be best. Zinsser Cover-Stain (oil) or B-I-N (alcohol) should be readily available at most box store and many real paint stores.

If you want a smooth finish without spraying you should follow a few steps. Prime, sand, prime again if needed, and sand again. Sometimes the substrate will really soak up the primer. You want a good blocking coat to sand smooth so two coats of primer may be needed.

After that, be careful with which paint you choose. Something like SW Duration is NOT a good choice as it uses elastomeric resins, which are too rubbery for a good finish. You want something fluid. There are some products like Insul-X Cabinet Coat (owned by Ben Moore not I believe) that are made for this application. If you need to use a more available paint, make sure it's 100% acrylic, not a vinyl/latex blend. Pure acrylics cure harder. You can modify the paint with an extended such as X-I-M Latex extender to get a more fluid application from the paint. Roll it on and immediately back brush to smooth it out. If using the correct paint and painting all surfaces laying horizontally, it should flow out nearly as smooth as a spray application.

The surface im working on is already vertical. i did not have space im my garage to lay it down and work with it.

Im not opposed to using a paint sprayer.

A sprayer will definitely give better results in that situation. Drips are a real pain when working with a more fluid paint.

Thank you

Kiltz and then roll on some PPG emerald line of paint will last forever and can take a beating

I just did some panels in MDF and primed with oil based kilz. Quick sand between coats and the color coat went down as normal. Just used 4" rollers

How’d it come out?

It looks great. Just like the real wood next to it.

Generally speaking, when I have a paint question, I'm not sure of, I go to a local Sherwin-Williams store and tell them what materials (the MDF in your case) I'm using and what sheen finish I want.

If you don't want to do that, then as others have said, an oil/solvent base primer is what you want and both Zinseer and Kilz make it specifically for MDF. If you have to deal with edges, it's a good idea to use spackling on the edges, sand smooth then prime. Edges of MDF are porous and soak up paint and don't always give you a good finish.

Have you thought about using Formica? might be a good way to keep the uniformity and protect the bar surface as well.

If it’s a bar, whatever you use, it’s not going to hurt to put an extra coat of polyurethane on it. MDF + moisture = not good. Too much moisture and you’re left with a giant pile of soggy cardboard. Can be gloss or satin, whichever you prefer, but the extra water protection won’t hurt.