Re: in advance/beforehand
It's not the "thanks" that are important -- it's knowing that what was written was understood and was helpful.
The person can "like" or just write "Got it! " and we'll know.
I also have no problem with "thanks in advance." I use it at work all the time, and I always respond after the person has sent whatever I've asked for with another thank you.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.