I definitely think aliens exist. They are probably too far away for us to detect though. The universe is still pretty young (there are more stars being born than are dying) so it might be that a lot more intelligent life will exist in the future but it just hasn’t had time to evolve yet.
I think it’d be very strange (and a little scary) if there weren’t any other life in the universe. As for where these aliens are or when we’ll find them or what they they look like, I have no idea! The most likely situation is that when we find other life it won’t look like cartoon aliens, it’ll be more like microbial life (unfortunately). Finding intelligent life will probably take longer and require looking in more places. Even then, there’s no guarantee we could recognise such “aliens” as being intelligent!
It seems very, very likely: there are so many stars with suitable planets (e.g. ones with liquid water), and creating the chemical components of (our) life has shown to be easily do-able by chance… so it would be odd if we were the one time that it worked in the whole universe. But it might still be rare enough that we’ll never “meet” the others. It’s also less sure that we’ll encounter sentient life like ourselves: natural selection means that from microorganisms, it’s likely that larger ones will evolve, up to complex animals… but we’ve only got one example of a fully sentient lifeform (ourselves), so a bit more difficult to draw conclusions on how likely/inevitable that step is!