I'd say Northwestern Lehigh. I grew up there up Route 100 and 309 from Allentown and it probably checks your boxes for both farthest-out Lehigh Valley school district with some decent quality to it AND available acreage because it's four fairly rural townships zoned for acre-plus lots.

The issue with East Penn, Parkland, and Southern Lehigh is much of each has transitioned to more dense population on smaller lots due to public water and sewer unlike NW Lehigh.

Whatever you do, avoid Northern Lehigh S.D. with poor quality schools and very, very high taxes.