What is the frame you are working with? Given how inexpensive used mountain bikes are, you might be better off finding a higher end used MTB to turn into a touring bike. One with a good quality crank and derailleurs will save you quite a bit of money over buying new. Then you can focus on putting your money where it will do the most good (perhaps new wheels).

I'd focus on having a sufficiently low gear; high gears are not that big a deal as worst case scenario you just spin out as you sail along at a good speed.

I'd want higher quality derailleurs than acera. 7 on the back with a triple up front is fine for touring. Thumb shifters are still my favorite for flat bars.

Here is a Trek 930 in the Detroit metro area for $129; this is a higher end bike than the one you are working on. You won't have to upgrade the parts:

https://detroit.craigslist.org/okl/bik/5896470038.html

This Nishiki is pretty cool; it's an old MTB and those often make fine tourers with longish wheelbases:

https://detroit.craigslist.org/okl/bik/5884531435.html

I'm a big fan of vintage MTBs as they make great all purpose bikes and great touring bikes. Given how cheap they are, you're just better off starting with a relatively high end bike with high end parts.

I picked up a 1987 Specialized Stumpjumper Comp with a nice tange double butted tubing set and a full deore xt group for $125. I converted it to drops with 3 x 8 gearing and bought new wheels. It's my primary commuter and I'd have no hesitation using it on a tour: