I've known a few people who use Co2 ONLY during flower. I'm way too new to give you advice on how much via your planned method however.

My long term goal is a generator with a PPM monitoring system. In that case you'd go somewhere close to 1000ppm. I can only hope for you, in that someone knows how much a kerosene lamp can generate. Once you know that you could figure it out easily enough using the timer method I'd think.

You may also look into the enzymatic CO2. It's available on e-bay. You mix water and glucose, then add a packet of enzymes that generate CO2 as they eat the sugars. In a plastic 2 liter bottle, you can run a hose off the cap to release the CO2 directly over the plants. When it stops working, you add table sugar to new water and put some of the old fluid into the new sugar water and the process starts over.

As for the Temps. That is a bit cold. I'd say get those temps up to at least the high 60s. This isn't too likely to kill them(grown plants), but it will stress them and could reduce yield once you start flowering. It would also slow new growth in fresh cuttings for sure. I seem to remember cloning temps should be close to 80 deg F.

Good luck!