just my opinion here: Dont start this process before you go.
As of right now, you are looking at a minimum of 6 weeks time for a First Adult Passport…and until it passes 10 weeks processing time, HMPO wont consider it unreasonable
No, your documents DO NOT get returned until after your passport is issued – typically 2 weeks after according to HMPO
Also, if you are inheriting citizenship through your mother, it is very much dependent on whether you were born before 1983, or after…if its before 1983, I might be able to shine some light on this for you…
But before that, IMO, if you have a valid US Passport for travel right now, use it – then apply when you return, or from the US, when youre not in a rush…things just seem so hairy at HMPO right now, call them 3 different tines and you’ll get 4 different answers.
Good Luck!