I'm going to do a bike tour in the 3rd world soon and I have some questions:

I should get 26" rims, right? I have a cheap bike with 28" ones now, but I'd rather do a quality upgrade to save myself trouble down the line.

I'm willing to spend like 1500$ for a quality bike if necessary. Do you have some suggestions for bikes with frames for 26" rims? Or should I order parts seperately and ensemble them?

Are steel frames important or is aluminum sufficient? Does steel frames have longer lifespan? I'll probably be doing more riding after this tour.

Could I check secondhand stores for bikes with steel frames and built it up myself? Or are new touring bike frames of much higher quality? (I probably won't find anything in the stores here anyway as I live in a small town).

Is important to have a well fitting frame? I'm 175cm but have long legs, my current bike is 18" and it's one size too big for me on the bike size chart. Idk if a smaller one would be more comfy.

Should I use panniers or a bike trailer?

Should I use suspension forks?

I'm planning to go very far, as long as my money last (4000$). I'll probably do more tours afterwards as well. So I'd like to get quality equipment now to save me from trouble down the line.