Mountain Bike Custom Wheels

I want to build my own custom mountain bike?
it’s a complete bike I just want to customise it like change the forks, wheels, breaks etc. The make of the bike is 2008 GT womens avalanche 4 17inch frame. I’m just wondering if it’s possible to get back suspension or is it impossible because of the frame is not built in with one? also what would be good to change on it to make it proper good for difficult mountains etc.
Very rarely is it cost effective to overly upgrade a bike. I often compare it to putting $3,000 rims on a $1,000 car.
Adding rear suspension to a bike not built for it is a negative.
There come a a point where the upgrade is simply not worth it. yes, when some things break, you replace and and replace it with a better product, but certain things break, you need to consider options.
Front forks are 400.00 for a good pair.
Wheel sets can be $400-$1000
Cables, chains, pads, grips etc are all consumable products that needs to be replaced at some point.
Anyway – be careful upgrading.
Shickluna Bike & Fitness Buffalo NY

