Great Question Tim
Here are a few thoughts. You have a good budget and we would recommend a couple of option and not sure you need to spend all of it.
To tackle a couple of Boil in the bag problems. Anything with a membrane will get sweaty if the conditions don't allow the vapour to escape quickly enough and it condenses. This is a big problem at this time of year as the humidity in the air reduces the osmosis effect, which is that the outside needs to be dryer than the inside. Think car windows before air con.
For what you are doing, there are plenty of options. However if you are stalking, crawling you need a tough outer shell on both the Jacket and Trousers.
100% Waterproof, windproof: Seetex Membrane: - Both Lightweight and autumn winter and spring with layering for colder days.
Seeland Marsh is very tough and will come in around £280 for the set, depending on who you buy from. Marsh is a bit noisy though, so if you need silent, Seeland Exeter advantage has just arrived. Exeter Advantage is new and is alot quieter than Marsh, but tougher than its cousin Keeper. The trousers on each of these have the same welly flap feature. Price about the same at Marsh
We have had customers at the store, beating in both Marsh and Keeper trousers and have been really chuffed with performance. However you will get some snagging on the facecloth if you do bramble scrub etc. We recommend using a Creiff overtrouser or tregging for this kind of Beating though as you don't want to puncture the membrane to much.
Get a pair of non waterproof trousers for dry days and use with the Jacket. Harkila Ultimate Trouser, around £140 ish will be tough trousers, and lighter alternatives would be Harkila Trail at around £120.
You could also get a tough pair of Carhartt Workwear EB136 double front logger trousers in cotton canvas, moss green and these would work really well too for rough shooting.
If you want to give us a call we can send you both Seeland and Harkila Catalogues or have a browse online to see various options.
All the best
Andrew