I used to use night buses regularly, and have yet to have a single problem with them.

The routes are pretty simple - either it's a 24-hour route (like the 88) and so the same as daytime or it's a night route (like the N155) where it's based on the same route without the N, but with extensions to serve more areas. I used to use both to get back to Stockwell, although usually the N155, as it runs every 10 minutes all night!

Weekend nights can be a bit more drunky, but they're mostly (IME) full of people working odd hours.

As for opening hours, there is an unwritten rule that the later somewhere opens, the fewer seats and louder music it will have. There are 'pubs' that fall into this category, but they tend to be the 'vertical drinking' variety. I suspect that's the only way they can make money these days.

If you fancy a late coffee, though, there's always Bar Italia...