OP should separate his two problems, working first on learning how to replace a handlebar, shifters, cables, and taping. That is mostly just taking stuff apart and putting it back together. I don't think he is going to find someone to hold his hand on the journey he is contemplating. Get the mechanical skills first.
The handlebar and stem issue just takes money. I'm old too and am going thru it with one bike. I was sort of happy with a Nitto Moustache bar and upright stem. It is certainly beautiful but a little too upright and there are some limits on hand position and too much reach.. I switched to an upright suspension shockstop stem and 31.8 carbon bar. I am probably going to get a flat top carbon bar just for the more comfortable hand position (flat vs round puts less pressure).