From what you describe you need to take a course in RV ownership. Luckily, it's free but is self directed :)
Spend 40-50 hours reading over threads on this forum between the 5th wheel section and Tow Vehicle board.
Here's a class itinerary:
Weight rating for truck - GVWR, GCWR, FAWR/RAWR
SRW vs. DRW trucks
Types of trucks - mainly gas vs. diesel
Weight ratings for 5th wheel - GVWR, pin weight, dry weight, axle weights
5th wheel hitches, bed length, slider or non-slider hitch
5th wheel cost, brand, value vs. quality vs. weight
Purchasing RVs - MSRP versus what you pay (should be around 70% of msrp)
Buy or finance?
How to use an RV - shore power, battery power, generators, black tank, gray tank, city water, on-board water (and added weight), slide-outs, hitching and unhitching, A/C and heat, TVs and tons of other stuff I'm forgetting
There's just so much to know that one thread on a message board can't even come close.
One thing I've learned from RVing for 15+ years. I'm being paid handsomely for the hours I spend online learning. Paid in the form of money saved by not making costly mistakes. This hobby is expensive no matter how you slice it. The key is to minimize just how expensive.
The real good news is the learning is half of the fun.