Leaking Res flat roof in MN, USA. Material + repair/install q’s

I have about 600(30x20) sqft of low slope flat roof on a single story extension in the Twin Cities, MN. No idea how old it is. I moved in a year ago. There’s a somewhat minor leak tonight under where the extension joins the original house. This is the first observed roof leak by us though the interior below it hints at possible interior repairs in the past, so…. Anyway, It’s dark and still raining so haven’t investigated deeply yet but

1. NO pooling right over the leak point
2. Some pooling 20 feet away near the edge where the water drains to
3. Seems to be leaking roughly under where I thought I noticed some rough looking flashing in the past
4. there is moss growing around the area closer to the original house, near the area above leak point but in other non leaking areas too

Plan:

A) I plan to investigate pooling on the roof and clear drains. Is the moss a bad sign? Or, is it useful since I guess the moss takes the rain hits before the roof surface does? Should I clear it? After that, maybe I try a leak test with a hose?

If no obvious progress then

B) call a pro for repair help. Any recommendation for a straight up company that wont try to sell me a new roof, when like maybe this is just a repairable flashing or sealing thing? I just want someone to offer advice I can trust. This is my forever home and this roof will need replacing sooner or later, so yeah could be a repair today but new roof in a few years. Win my trust today, get my business tomorrow. Or something.

If I really need a new roof then

C) what is the gold standard for flat roofing material in MN given the temp swings. -20 to 105. Lots of squirrels and other animals will be on it. Also would like to walk on it too

D) what am I realistically looking at for rip and install of 600 sqft of EPDM, total cost?

Ironically I was pondering installing skylights in this roof. If I were to do that, and assuming I need a new roof, would it be better to install the skylights first and then get a new roof? Or the other way around?

Appreciate any advice!!