24 seems to be the number people call minimum. I usually use 24-30 in 2400pts games (I play under the ETC restriction, else I'd bump them up further I think)
I don't use temple guard, but if I was going to there would be 25+ of them with possibly the razor standard.
10 with a Slann is like the magic number for losing every single one to a miscast, isn't it? I've ran units of 10 solo as a hammer unit a few times. A few more attacks than 3 Kroxigor and one more wound. They don't move as fast though and can't stomp, but having 10 bodies means they can deny steadfast if you get a flank charge at full strength. But yeah, I think 20 is my minimum. I like 26+ If you only have 10, I would suggest using them as stand-ins for Scar-Veterans on foot until you can afford 10 more. Just pick out your 2 or 3 favorite and put them in the front row of a Saurus unit.
26 is my favourite. 6x5 with the slann in the middle. But since I've been doing slann in skinks behind my saurus and monsters they have been sitting idle
I go 5 + x where x is how many hundreds of points the game is. Thinking outside the box, 10 Temple Guard might be a good flanking force but it will not be able to keep your Slann alive nor will it be able to inflict or sustain a serious beating.
Thats what im planning on, i bought another battleforce and im use the temple guard from there and the slann to make a unit for a 200 piont esclation league.
In terms of size, once at 2500 points, run something like 36+ for a horde in four ranks and they rock and roll. It is ideal to have the TG unit wider than opposing units to max attacks in the front rank. Keep the slann on one flank of the second row to reduce the miscast damage and provide for more TG in the second and third ranks to get attacks on the target unit. Because slann miscasts can end up eating quite a few TG in a game, especially without soul of stome on the slann., putting the slann on a flank reduces the number of TG in base contact with the slann in the event of miscast rolls lof 7 or less. You need to numbers to survive the initial onslaught, most often hitting after opposing units, and to absorb the shooting and magic the unit will take wounds from. Also, with greater numbers the slann augments and hexes will matter more in extended grinding multiple rounds of combat.
The 36 is really because there is a good chance of losing 6 to 10 models before combat and with generally striking second or last, TG need to be bigger to hold up against stuff like executioners and white lions, etc, where they take a lot of wounds before getting to hit back. In non-comped and lightly comped tournament play, y9ou need the larger size to have enough to survive extended rounds of combat.
36 with Lord Kroak in the middle would be a blast I think. -1 to hit helps them survive in combat, unbreakable horde FTW