For seams -- I press open pretty much all the time. I have tried both seam open/closed over my years of quilting and for a lot of reasons, I prefer open. 30-40 years ago I was rarer, but with more and more home long arms, more and more people are discovering some of the positives and are joining me on the open side of the fence. Basically/short form, I feel side seams are an artifact/leftover from hand sewing and that with modern machines (including irons) our seams are tough enough to be open and are desirable for multiple reasons.
I do a lot of scrappy style work and I will mix fabric weighs pretty happily for the most part. Batiks and Liberty of London (lawn) are quite light weight but have a very tight weave with fine threads. BTW, when sewing primarily batiks I usually use a "sharp" needle, that is not a fresh one but a type, like Microtex by Schmetz.
Homespun tends to be a looser weave than standard quilting cottons and that can be an issue, but I typically match homespuns with a solid non-homespun cotton. I typically don't have any issues with wear when used in a mostly non-homespun scrappy quilt.