September is a great time to visit. Weather should be decent and warm. I only get to city around 2 or 3 times a year now, and September is always the one month I visit. Also go in March but its usually cold, very cold, and wet.
Get a membership. Get your tickets earlier and you should get 10% in the club shop and our online shop. Highly recommend a stadium tour, not on a matchday though for obvious reasons. U used to get a discount in the shop as well after a tour but not sure if that's still the case?? Haven't done a tour in years.
I've always stayed in a Premier Inn or a travelodge in the city centre. Basic but decent price. Use the tram to get around, easy and quick and good value for money I find. Prepare for a long wait after the final whistle though, trams get rammed. (Or leave early like a few others do, but that's not my thing if I'm honest). I've sat everywhere in the etihad and south stand is my preferred choice. Atmosphere is best. The only place I've never liked is East stand lower, just because if it's sunny then it's absolutely boiling and the sun is in your eyes the whole game. Wherever your seat is though you won't get a bad view, every seat has a fantastic view.
Plenty of shops in town, I enjoy walking around town, just be aware of the trams :-)
Will u be staying in Manchester? How long u over for?