$400 you can get a great set up.
Yes you need an UQ, for any Temps below about 65.
Warbonnet makes great hammocks, but weather or not they're the best is subjective.
You don't really need a bug net integrated. You can always buy something like a HUG (half bug net) from arrowhead equipment and put on any hammock.
Hammock is a personal choice, there are countless options. I have a Dutchware hexin 1.6, 11 footer. Awesome hammock. Dutchware has a hammock with integrated bug net if you so desire. Get one of his suspension systems with the hammock, I prefer cinch buckles. There's your hammock and suspension for about $80.
For an under quilt I'd get an Arrowhead equipment jarbidge. It's 3/4 length and rated to 25 degrees. Get a small pad for your feet since it's 3/4 length. Cost with a pad, $105
You can save $50 and get a Snugpak underblanket if you so desire. On amazon for $53.
For a top quilt, you can spend a lot, but a cheap option is a Snugpak Hammock Quilt. About $45 on Amazon.
You could get an Arrowhead Equipment top quilt if you wanted. They are about $160 though. You'd still be under budget with it.
If you got the Dutchware hammock, and suspension, with the arrowhead TQ and UQ, you'd have an excellent setup that would last for years.
If you got any of the Snugpak stuff, you'd still have decent gear, just a little heavier and bulkier is all, and you'd save quite a bit.
Either way, you're under budget.