1) Performance is getting better slowly and is quite a lot better since release but there is still a long way to go. PvE works fine without any lag but PvP can be extremely jumpy at times, although they have fixed just about all the "out of sync" issues for PvP which is really nice.
2) There are still quite a lot of small bugs that will generally be fixed by exiting the game and starting up again, all the game breakers I encountered early on have been fixed. You will notice the bugs along the way but generally they won't effect you too much. If somethings really bugging you just ask in chat as there is generally someone around who knows how to help, plus there is the technical support section of the forum which does an amazing job.
3) The population is not huge, it is growing, but not huge. You will generally find people talking in chat and if not saying something in chat will usually get a conversation started. Finding PvPs can be tricky, as I have finished everything else all I do is PvP. I can't find PvPs every time I log on but it does depend on the time of day with different parts of the world being asleep etc. That being said if you just got the game you wouln't want to PvP anyway as you would have a very small amount of units and if those units die in PvP they are gone forever. There is also a newly introduced newby protection but I'm not sure if you can opt out of that or not. Also you only get matched with other armies/towns of a similar strength to your army so being able to search with different strength armies increases your chances of finding a PvP.
That being said I love the game because it really is unique and epic! I play other games too but always find myself logging into DoF to search for PvPs and talk in chat while I wait, or to try convince someone to fight me
The PvP is very laggy and jumpy but after doing hundreds of them I have gotten used to it, plus the rewards for PvPing are awesome. The devs are amazing and so is the community generally so the game is improving all the time. Also there is no sunscription fee so if you buy the game now and don't like how it plays you can just come back in a couple months! If you read all that give yourself a pat on the back... xD