Pattie: You have a big as well as multiple questions. I can contribute only a little of my experience.
1. Pretreatment: some seeds need chill treatment. Some need soaking in water. some need to be sanitized to kill moldy surface.( make sure the seeds are viable, otherwise there are possible some immature or underdeveloped seeds)
2. I use 50% by 50% of ground peat and perlite. The wet mixture is well heated in microwave. Mostly the media is for germinating my camellia, peony, gardenia and Wintersweet seeds.
3. I tried it on M. champaca and produced a few very weak seedlings. Now I use approach grafting. It is much easier and quicker to produce larger plant. There are at least 9 Grafted plants in the process in my yard and I shall have 9 good size M. champaca plants ready next year.

Thanks longriver, not sure if I'll have luck with these seeds, but would love it if they grow for me. Are you trading or selling your grafted plants when they are ready? Would be interested in either case. Thanks again.
Pattie

Pattie: Sorry I do not trade or sell. Besides my young grafted plants need special care. It may take additional 3-4 years to become a strong production plant. I am still building my stock to a number, about 20 plants. Sometimes the freeze might kill 1 or 2 my plants. Two years ago, I lost 4 plants due to 10 continuous freezing nights. I have to move my plants in my living room in case of sub-zero degree.

I know that people in Canada manage to grow M. alba.