All the newmars are heavy. I have a Mobile Suites. Very similar. The best indicator of a quality fifth wheel is to look at the front. If the area from the roof down the front and back to the rear of the over hang and then down to the bottom of the unit is one solid continuous pice of fiber glass with no seams that wraps up to the sides that is a quality fifth wheel. It is built to last. I suspect the Newmar you're looking at is made that way.
As to brakes the best way to repair them is to replace the whole brake plate. Look on line at most any RV parts place and you will see what I mean. I'm not sure on price but I think they are reasonable if you do it yourself. I'm thinking less than 100 bucks a wheel. If you take it to an RV shop then it's like the class A, you had, outrageous. If you can find an independent shop that works on "trailers" not RVs you can possibly get it done reasonably. But, it is a very easy chore, only four bolts and some wires involved on each wheel. The hard part is jacking up the trailer.
I think though you might be over thinking the brakes issue. Most people who tow these heavy fivers like Newmars keep the brakes working good. So, someone owned that unit and pulled it to where it is, chances are they took care of the brakes.
Tires should be the very best you can buy. I'm not sure what's on it but I would suggest 17.5 inch trailer wheels with 14 ply trailer tires. I came to that conclusion after a summer with two blow outs on 5 year old goodyear G114s. It was ugly, the first one took out all my systems up under the slide. Took a weekend and about 25 trips to Home Depot and the place that made the gas hoses before I got it back on the road.
Hope this helps and welcome to the fifth wheel world. I'm sure that if you are looking at a Newmar you have your truck properly set up for that weight. If you're not sure try looking on one of the forums for your brand of truck. For Ford I can suggest Ford Truck Enthusaist. Just google FTE. Dodge and bowtie have similar sites. I suggest you don't discuss towing weight and truck rigging on RV forums. Those threads always seem to become 20 pages of hard wired opinions. Go to the truck forums, you get much better info on that subject.
Stanley Z, Beautiful Sharpsburg Ga.
2014 Ford F350 DRW with a little bling
2005 DRV Mobile Suites 36TK3