Our rural electric Coop is REAL good with this and would answer all your questions, hope your power co is to

From recent dealings after the meter is all you and ours would do it and bring pole

you should be able to go to just house meter for all use

the biggest problem with 3ph. is getting it TO the yard, once you have it there I doubt they would downsize your transmission line

you should be able to return to 3ph anytime