If your building a 308 Win, the 300 SAUM bolt face is to large as it is cut for the larger magnum bolt face of the fat little round.
As said earlier, any 700 receiver will work as long as it has an 308/'06 size bolt face, OR SMALLER.
Remember, it is a simple task to open up the bolt face on a 223 size bolt for the larger 308 sized bolt face and to fit a Sako extractor which is a better extractor then the factory 700 style.
For a single shot, it really does not matter if you go long or short action to be honest. Some will say the short action is stiffer and this is physically true but with a single shot insert fitted to the receiver, the long action actually has dramatically more bedding surface then the short action as well as a wider wheel base between the action screws so do not count out the standard action Rem 700 if you find one at a good price.
The single shot inserts I use perfectly match the bottom contour of the Rem 700 receiver so you can bed teh entire length of the receiver which greatly increases stability. The insert also increases the stiffness of the receiver in both short and long action, as does using a one piece scope base.
Just remember you need an '06 bolt face, 25-06, 270, 280, 30-06, any of these are what you are looking for.
For building extreme accuracy rifles on the Rem 700 action, I much prefer the ADL receiver even if they are to be converted to single shot. The reason is the stock design is much stiffer in the mag well area then an open bottomed BDL design. Also, these receivers are less costly then the BDL but the receiver is identical dimensionally, only difference is how the mag box is attached to the receiver on the ADL and floating on the BDL.
Only problem is that the selection of stocks suitable for your needs and inletted for the ADL are relatively few. I do not believe H-S makes a tactical style stock for the ADL receiver.
McMillan does, hell, they will inlet damn near any combination of componants you can think up but you pay more for them.
Holland Gunsmithing offers a Laminated wood stock that is built to heavy dimensions and is a top quality stock for the ADL. Besides the McMillan, the Holland is the best long range stock I have found for the ADL receiver.
Here is a pic of one of my APS V-Block rifles using the Holland Signature Heavy Varminter stock. This a fast twist 22-6mm AI with a 30" Lilja
I would stay away from the B&C stocks. They are decent stocks for a conventional range big game rifle but you are asking more from your rifle, it needs a top end handle.
Barrel wise, your first two listings are great, Krieger and Rock barrels are top notch. I have used and fitted the Kriegers and they are great barrels. The Rock barrels I have not used but I have talked with enough fellow smiths that have used them and heard nothing but good about them.
Shilen "Select Match" barrels are pretty good but for the money you can get a Krieger, Rock or a Lilja which is my prefered barrel. I feel these are better quality barrels as a hole.
Douglas barrels again, if you get one of the XX Air Gauged barrels it will probably shoot very well but again, the other top end barrels are what the best of the best are using so there must be a reason and there is.
Aftermarket triggers are a good idea if you want to take the pull weight of the factory trigger below 2.5 lbs. This is the limit I will tune a factory trigger to in my shop and only if it proves to be safe and consistant at this pull weight.
Most Rem 700 factory triggers will go down to 2.5 lb pull weights and stay very consistant and be safe, but some begin to get pull weight variations and safety issues when tuned this light.
FOr true long range shooting, I like a pull weight in the 1.5 to 2 lb range. If the rifle is a dedicated extreme range varminter or paper puncher, I will go to 6 oz with aftermarket trigger.
If the rifle will be used for big game hunting at long range, I do not like anything under 2 lbs especially up here in Montana and the northern states where it is generally cold during hunting season. A gloved hand or a cold bare hand will not feel a sub 2 lb trigger well enough to control the shot.
Again, this is only my recommendation to my customers, they are the boss.
If they do want a lighter trigger they are warned of the dangers and an aftermarket trigger is ordered to be fitted to the rifle.
Jewels are the standby aftermarket trigger for best performance but the new Rifles Basix triggers are really getting a good name as a quality trigger and at around 1/2 the price of the Jewel.
I have a 2 to 6 oz Rifles Basix on my 2000 yard rifle in 338 Kahn which I adjusted to 6 oz, I like to at least feel the trigger before it goes bang. It has been one of the best triggers I have ever used for extreme range shooting.