Sounds like a good soil mix. Don't listen to MG haters. I've used it and I like it. Trust me and your Aunt not RIU Newbies. The only thing is it can be hot for a new seedling but if you havent seen burnt leaves by now you may not see them at all. That your 17 day old seedling isn't growing very quickly doesn't worry me and it shouldn't worry you. Trust me, it's growing in the pot and that's all I'm concerned with.
So you fertilized with diluted MG, that's good, don't think it will have an immediate effect. It takes two weeks for the plant to respond to many things.
The little mulch layer on top is fine, it keeps in moisture to an extent. And as it breaks down it will release Nitrogen into the soil in time.