Sounds an exciting new venture, how nice to have a heated propagator in the GH. Mines, an indoor window ledge type, so this doesn't answer your question but I agree with LearningSlowly, no matter how tempting it is, try to hold off germinating to soon. I learnt the hard way and am still learning.
I keep a gardening diary of when early seeds are sown and whether the plants grew or not, which has been useful for stuff which needs a long growing season like peppers, chillies and aubergines. Was going to start sowing aubergines and peppers a week earlier this year.
You might want to keep a dairy to include temperatures of sowings, then you'll know for future years which you've tried and what works, usually the seed packets say at what temp stuff germinates but sowing times can vary as to where you live in the country.