I can get the temp to low 30s if necessary. My main concern was that I lose the yeast permanently if that can happen.
So, I can chill, add gelatin, let sit in cold for as long as 3 weeks, then warm for a bit to normal fermenting temps and add priming sugar and bottle. Then 2-3 weeks in bottle before refrigerating for drinking.
Sound good?
I don't see a problem with it. A couple of comments, though...
Low 30s is good. I take mine to the mid 30s mainly because with my setup the inside of the fermentation chamber ("FC"; a freezer with a temp controller) has some pretty good temp swings and I get a range of temps that's usually down to -3F from the temp the controller is set at. This is using a thermowell, which takes the temp readings from the center of the fermenter. I've heard/read that as close to freezing as possible is best, without actually freezing. In my particular case, the issue is the swings, so I stay away from setting the controller too low.
I've never used gelatin, so I can't help you with that.
It's the length of lagering that will determine the activity of the yeast once you bottle. I'm doing a Kolsch right now that I'm lagering for 4 weeks. I don't expect that to be a problem when carbonating in the bottle, although it might take a little longer than the usual 3 weeks. You should be OK with 3 weeks cold conditioning. As for longer, again someone else may have to chime in if they have experience with that.
But here's a cool (pun intended) thing: Don't let the beer warm up before you prime and bottle. Cold liquids hold gas better than warm liquids (Boyle's law of gases? Maybe not...). You'll notice that carbonation charts call for less priming sugar the colder the liquid is. This is because cold beer, even though there is no fermentation going on any more (or hardly any), *is* carbonated to some degree. So it takes less priming sugar and, presumably, less time, to carbonate in the bottle if you prime and bottle the beer cold.
What I do is I leave the beer in the FC until right before I bottle. By the time I rack and prime, the beer is probably sitting at around 50F (my guess), so it's still cold enough and hopefully still holding CO2.
The effect? In addition to less priming sugar required to yield the same volume of CO2, it should take less time to carbonate and the lagering period's effect on yeast suspension becomes less of a factor.
Your mileage may vary, of course. But that's the theory I'm going by. You may want to check out some info/charts on carbonation. But the bottom line is: bottle cold.
Hope this helps.
P.S. Bottle cold, then let the beer come up to 75-80F for natural carbonation.