Hello and welcome back!
Allods is still a great game, just as it was back when you played. In order to experience the game most similar to what it was back in the old days though, I do strongly recommend the P2P server, so I'm glad that you decided to try it out. You might only get disappointed if you try the FP2 server, but it depends whether you care about P2W or not. If P2W is not an issue, then you'll most likely enjoy the FP2 server more as it has a higher population.
There are active international guilds on both factions that I've heard good things about. On League side you have "Ze beer", which seem to be a mix of mostly French/Turkish/English members. Then you have the guild "Omniscient" on Empire side, which seem to be doing very well currently with many active members. I think they have both NA and EU (English speaking) players.
To answer your question "What should I expect?": You should expect a very lonely leveling phase probably all the way to max level, since most active players are already max level. You should also expect that you'll sometimes have to wait very long for battlegrounds to start, because of the low population. In short words, expect a low population and downsides affected by that. Other than that, expect a fun time with your future guildmates and the good feeling of enjoying a great game