You could use the existing forest or just build one forester's house. One should be enough, so that forest shouldn't be that big. You're gonna have only one Temple, so you won't need much meads.
Indeed, but having as much farms as possible is really important in RttR/S2. At least in my case this would result in me not building temples, since focusing on recruiting/promoting will be a much better way to win the game. So I think I would only build temples on ridiculously huge maps where you can produce an excess of food.
I agree about gfxs but from my point of view the temple which requires only one ware (pigs) could be too cheap. But it also depends on which option for soldiers we are going to choose.
I don't think pigs are too cheap, because you would still need about 2 pig farms for supplying the temple with enough food. The pig farm will need something like 4 farms + 4 wells to be properly supplied with wheat/water. So apart from building time you'll still need 26 boards and 18 stones (without the temple) just for the necessary pig supply + lots of space. This makes a total of 6 large buildings and 4 small ones just to supply your temple.
Additionally, the pigs which are sacrificed will reduce your food production capacity. This means you won't be able to supply as many mines as you could without a temple, although this really depends on the ware you choose. If a 2nd ware is really necessary, I think it should be an abundant one like coal/wheat/boards or granite.
It is really a difficult choice to make it not too easy, but not too hard either. Making it too easy will result in abusing the new temple mechanic, whilst making it too hard will result in players not using temples at all. So adding a 2nd ware will make it even harder, therefore not worth building at all.
I really like the temple idea so IMHO it should be worth building in every game, not just in exceptional cases.