Rifle re-build

[SLDPULR]

So the time has come to re build my rifle. The rifle started out as a Remington 700 ADL with factory slim profile barrel. I bought a action wrench and barrel vise from MidwayUSA. I took the factory slim barrel off and bought a take off 20" SPS tactical barrel. I ended up having to buy a chamber reamer and take a little bit out for the go gauge to close on it. I bought a used SPS Tactical stock and BDL floorplate and trimed the ADL box magazine to fit into the new BDL floorplate. I picked up a cheap 8.5x25x50 sightmark scope Leupold rings and base and got it all put together. I Have put about 500 rounds through the gun shooting 200-600 yard targets and now I'm hooked. This rifle was a budget build to see if I would really get into the long range shooting. Now that I know I like this more then my mid range AR's I want to build a good long range rifle. I took the rifle back apart and had the action squared and the threads cleaned up. I really just want a bench gun that can reach out to 1000 but I want to build it. My question is where can I get a short chambered 24-28" threaded barrel. I have found a TON of places that make custom barrels but I'm looking for a kind of a "off the shelf" barrel. I still have a lot to learn about what twist would be best for me and any ideas would be greatly appreciated. So here are my main questions....

1. Should I put a expensive custom barrel on a cheap Remington 700 action.
2. Where can I get a short chambered 24"-28" Heavy threaded barrel.
3. What twist should I go with. (or any reading info on the subject to help me decide)

I have been looking at a a few diff options for stocks like Accuracy International and Bell and Carlson but want to get my action and barrel together before I get the stock. I'm a newb when it comes to bolt action rifles so please take it easy on me. Also Happy New years.....

Colt