I'm familiar with the marina. The channel in can be nerve-racking, but it's well charted. Keep the charts out at the highest possible scale/zoom level. Do not stray from the channel. You will pass visible rocks that you could almost reach over the side and touch, and seagulls standing knee-deep on the mud flats just a few feet away.
The marina is mostly smaller boats. There's a good restaurant on site, and an ice cream store across the street. I'd call it a rather long bike ride into town, but maybe a pleasant dinghy ride.
I haven't been there lately, so I can't answer to the amenities. Based on the small-boat focus, the long ride in, and the distance from everything in town, it wouldn't be high on my list, but your priorities may be different. A better option might be to take a mooring at Pepperell Cove on the Kittery side, or check with one of the yacht clubs on the NH side, maybe they offer moorings. If you've got to dinghy to town anyway, you might as well be closer.
The current isn't as big a deal as you'd think. You just approach the mooring or dock into the current. If it's a finger slip like at Prescott Park or Badgers Island, you might want to wait for slack or get some help catching lines.
The docks along the Portsmouth stretch, on either side, are subject to frequent large wakes during the day. That may be a deal-breaker for some.