Woah, if you're asking how many it will hold, then you must have a lot of buddies....LOL!!!
I might be too late for the party, but I've had eight yard birds in my SV-24, which is about 1-1/2" wider than your rig. 300* is about right. Use the 2nd and 4th grate positions (from the top down, this leaves some head-space so they aren't touching the grates or cabinet above) with 4 per grate, avg weight 4.75-5.0lbs, arranged something like this:
I had room on the sides, so you should still be able to fit 4 per grate on yours. Keep in mind that unless they are very big eaters you only need 1 per 3-4 guys, otherwise 2 per person if big eaters and not much for sides.
Times will vary depending on the smoker and other conditions, but I always cook to temp...minimum is 165* but I like to take birds to at least 170* in the breast and a bit higher in the dark meat...which ever comes last with whole birds. Internal temps are everything...you'll know its cooked to safe temp, and also know it's not overcooked and about to became shoe-leather. Generally speaking, you won't start to suffer the dry bird syndrome with skin-on whole birds until well above 185*, so don't worry about that. You can expect close to 3 hours (EDIT: I've seen 5-6hrs), but you may want to rotate your grate positions at least once during the smoke (about 1/2 way through), top to bottom, along with front-to-back (180* rotation) to keep them cooking more evenly. Loaded vertical rigs tend to buffer the heat and smoke getting to the food above, that's why I rotate grates.
For grate/chamber temp monitoring, having four birds per grate on 2 positions, a centrally located probe seems best, but just below the upper grate would give a good representation (center of grate, between the grates). You will probably experience higher temps around the outer portions of the grates, depending, so this will monitor your coolest area of the cabinet. Be sure to leave at least 1.5" or so between the birds, and don't crowd them too close to the cabinet...that's the hot spot, and they'll over-cook in that area. You can also rotate the birds 180* on the grate (once, when you rotate grate positions) if you really want to keep things cooking the most evenly.
Oh, if you're smoking anything else at the same time, you may opt to put it above the birds, just so they don't get more heat baffling, especially if it's large or in a pan...just think about how the heat has to flow through the cabinet from the bottom up and you'll know what needs to be done.
Hope this helps....enjoy the smoke, friends and food!!!
Edited by forluvofsmoke - 6/19/15 at 8:25am