Hi!
I would be cautious of slant shank machines for ad-hoc craft purposes, because the needles is at angle (hence the slant shank) because the angle means the needle has to travel through more of the material than a straight shank so needle breaks and penetration issues might be more common according to Helen Howes and to be fair I have had some issues with more layered projects, but I don't push the 500 too hard.
A 15k with a zz attachment might not be a bad bet.
319/320ks they are lovely, I've heard good things about them, but they're almost redundant because the correct needle system is only being made in 2 sizes and costs £1 a needle or more. Retiming to 705 (standard needle) is supposed to be possible, but I haven't heard good things about that approach from OSMGs, my local OSMG mentioned another route he was exploring but I don't know if he was successful.
216g might be worth a look, that has some ZZ and is supposed to be very sturdy pfaffs 130 131 260 and 92 (concrete grey box) might also be good to keep an eye open for Crestas (sometimes called lada maybe 132 (like in my signature) they have a reputation for being a solid stitcher and are somewhat sought after.
Or the 15 with a zz attachment they are very tough and easily sourced, but more limited on the stitches.
Hope that helps