1. I would cover the entire seed... but don't remove the seed to do this now - just tear off a LITTLE bit of the rock wool and cover it otherwise, you could damage the root
2. I don't think pH really matters at this point but it's good to get in the habit of giving it 5.8 or even 5.5 right now and increase it to 5.8 when the roots touch the water
3. You want really high humidity from now until the seedling is about 1-2 weeks old... 70% is good... then start lowering it to the 60s... then 50s in pre-flower and early flower and then the 40s in full flower...
Good luck!