So i am a tech guy, sit on my ass all day at a computer and then again when I get home. I recently passed my driving test and now looking to get a gym membership.

My plan at the moment is on going to a 24hr gym around midnight as this is the best option, other than going at 5am. I am a 21 year old who has a decent size beer belly, I drink a lot and want to do go to the gym to get fitter and also build some muscle mass. I am a broad shouldered manlet at 5'8" and will be going alone.

So what I really and interested in is;
Best time to go? Morning or late, late night?
How to overcome the anxiety?
Will weights and such help rid my stomach, or will I have to do a lot of cardio? (I enjoyed the rowing machines back in the day, but running is a no-no due to bad knee/ankle from football aeons ago, this is why I ask)
Is there things I can't do going alone? Should I try and find a gym buddy? (I enjoy pushing myself at tasks, so I expect to constantly try to up what I can do)
Is an hour a time a decent work out time? I expect this would be what I aim for?