100% agree with Saddlesores on both these points.

Bottle cages? I had 4 attached to my Trek MTB. Now I use 3, 2 are the XL size. There are only braze-ons for 2. I also have my pump and Click-stand attached. Truth be told, in Europe I've never needed to carry more than a couple of liters of water, unless wild camping. Even then, water is everywhere! If you're hitting a desert, then maybe you need extra water - but bladders in a pannier I think would be better.

More importantly, if you like your MTB for touring and the rims are the issue.... then get new wheels.
I tried the original wheels on my MTB when I loaded it up, just to see how they handled. The front was ok, the rear failed slowly under the weight. I'm not into ultralite!

I got 2 new 26 wheels from SJS in UK. Front wheel with Son Dynamo. Spare spokes ordered at the same time so I have everything I need for repairs. Very reasonable prices (I thought) and quick shipping. I live in NL, by the way.

I get the feeling that you're new to touring? If so, the most important thing to remember is to tour! Whether that be 1 day, 1 week or 1 month! The more you do, the more you will learn about what is important for YOU!
I'd advise spending as little as possible until you know what you want.

Sounds like you need new wheels for your MTB anyways, so I'd advise getting (touring quality) wheels. If you upgrade your bike you still have the wheels!

Happy Touring!

Frank