Hey! Welcome back!
Most of the players here are in exactly the same boat as you, used to play either Dragon or Phoenix servers on Euro Mir and decided to have another go.
Rest assured this server is very active, in recent weeks we have seen peak numbers of players online at one time hit 170.
Around 2 years ago I was in exactly your position, it was overwhelming at first but you soon get over that. The game is really well set up to encourage "catching up". You can type @under120FreeXP and it will massively increase your exp rate that you get from killing mobs. You'll need to keep retying it as it turns off every time you log in or level up.
Doing the starter quests (Emily npc in Border village, just near where you start) will not take long and are really easy, they are just enough to remind you of the basic controls of getting around and doing things. By the time you've finished those, you should be around level 40-50. Then get to BW and find the Farmer (just east of central safe zone) and try some of his quests, they will be a little harder but have massive experience rewards, you should be able to reach level 80-85 by doing these quests.
Take your time and explore your way around, there's no rush!
The main differences you will notice is obviously a lot of new items, that can be quite overwhelming but don't worry about it for now, you'll learn about these in time. Also how you move around, you don't need to run everywhere any more, every town has a portal that allows you to instantly move to other towns and to hunting areas in that province. Portals unlock when you are level 50, so finish those quests then go exploring! Also at level 50 you'll get access to the home key, press H at any time for a popup you can click on to teleport back to town, always handy if you forget to buy a town teleport scroll.
Also, how players buy and sell stuff. You'll notice stalls around, players set these up to show off what they have at a fixed price. There's also the auction house, where players put things up for sale, click the blue house icon near the bottom right of your screen to open it and search or browse.
You'll probably find some players offering to give you a lot of free stuff or boost you to higher level by taking you to a high level hunting area for lots of experience, but I usually discourage this until you are more familiar with how the server works, as higher levels are more difficult to play, so skipping the easy bits will only leave you unable to progress properly on your own so you need more help and it's a vicious cycle.
Do have a look over my guide,
[Guide] Zade's nooby wiz guide, some of it is now inaccurate due to changes that have happened in the game since it was written, but it's mostly still very relevent.
There's plenty people willing to help out with answering questions if you have anything specific you're stuck on, you can ask on your starter guild (every new player is added to a default guild, so they can talk to other new players) use !~ to talk on guild chat and maybe someone will chat back! Or shout in BW with ! before your message, there's usually plenty people around, or pm me on one of the characters in my signature below. I'm quite often AFK so apologies if I take a while to respond, but I do reply to as many messages as I can
All the best and good luck with your adventure!