>>1599979that new fork looks great dude. Better than stock maybe. Even though it's unicrown.
sure try upright bars.
but i wouldn't limit it to moustache bar ones. other comfy cruiser type bars are great.
Go to a bike kitchen type place and try score some nicer canti levers and thumbies. Those are common takeoff parts and will work well with what you have. Look on aliexpress for bars. Aliexpress sells lots of decent velo-orange ripoffs. Aluminium bars typically are better.
You could do big riser swoopyboys and keep your stem even, just shim it to 25.4
and yeah, your road levers will -work- on anything with enough of a curve to put them on. Put if you go really high you'll probably want to recable anyway so in which case why not swap to flat bar levers? Better ergonomics. I'm not a huge fan of moustaches. I don't see them as superior to drops. You could just as well simply put on a technomic stem instead of that.
I think it's a good idea in general to try old road bikes with cruiser controls, even if you change back after a bit. You'll have your fun. It's not expensive if you go used parts and aliexpress instead of like nitto and VO and stuff. And consider just leaving the downtube shifters. If it's a cruiser you don't need to shift much. Makes it easier to go back.