So, I also find 4x5 contacts a bit too small for my liking. 5x7 however is a really, really nice size.

4x5 will be easier to enlarge as those enlargers are all over the place and easy to find. 5x7 will require an enlarger designed for 5x7 or 8x10. Either way, it will be huge. and expensive. and more likely, very rare.

Either will scan fine, and I use a sheet of AN glass to keep the neg flat. That method does introduce four more sides to attract dust, but the upside, for me, is a very flat negative.

Scanning will be the easiest path and allow you to scan up to 8x10, presuming you get at least a v700. Contact prints may be more rewarding, if you like the idea of craft.