We are planning to go FT in under four years. I have been advised in a lot of other forums and here, to look for a good used Fifth Wheel at first. A lot of Fifth Wheel that are for sale that are unused or retiring so are usually in good shape, and have all the bugs worked out. You just have to search. A lot of comes down to cost to start up FT ing, as they depricate big time once you buy new. You will soon find things about your Fifth Wheel that you like or dislike or wish to have. Then later on if you like the FT lifestyle you can move up and Buy the unit you want with what you want, and will have a trade.
I have been told the same about the length of the Fifth Wheel. Just get what you want. Personnely i like mine at 33' to 36'. I like to visit NP's and SP. Just my take.
The Truck should be a 350 or 3500 your choice DRW. Should you want the SRW than that will limit you Length/ Weight and options you want in your trailer.
Hope this helps. Best of luck.
Scott Stielow IC1(SW) USN Retired