IMHO, people who buy end of year sales RVs pay more than those who custom order exactly what they want never walked in from a few of the so called wholesale RV dealers in the midwest. If you want new, buy new. IF you want new, discounts should be on the order of 30-40% off MSRP. So you find something that is listed at $45k, that should be closer to $30k. I cannot think or anything TT other than Airstreams that should cost you more than $45k OTD. MSRPs are getting into that range, up too $50k. 5th wheels can easily exceed $45k OTD.
Floorplan/floorplan/floorplan. Find the one you like. Once you do, you'll find something like 15 brands/models of various prices and minor differences to compare. If you are starting online, pick higher sales brand like Keystone, Forest River Inc, or Jayco and browse the various floorplans.
5er vs. TT - There are general floorplan limitations for one system vs. the other, but generally you should find something that you like in either group. Pick the style based on number of entry steps, interior height, storage, use of truck bed, etc. They can both tow well. You have the truck for either type, although I will warn a 06 2500HD payload can easily get eaten up with a family and 10k pound 5er.
I would advise against a toy hauler 5th wheel. You have a toy carrying space - the truck bed as long as you tow a TT. Toy haulers cost more than similar sized/featured TT or 5er non toy haulers. I don't see it making sense in your budget, at least new.
For your specific requirements, here are a couple floorplan ideas. This is a variation on my favorite one. MAster bed on a slide, lots of space. 3-4 bunks depending on if you want the outdoor kitchen or not.

This one became very popular 3-6 years ago. Access to the various spaces/fridge/pantry/bathroom with the slides in should be considered if it will be important to you or not.

And this modified version of the last one with different bathroom access and island kitchen.
