A suggestion.
You should implement a magic room, that has a transmution tablet, energy condencer or other things magic, near the machine rooms. this would help for people who aren't wisards yet.
I'm surprised that the server actually has so many people on it. Every server I've been on has less then this one and they don't fill it up. At least there are lots of people to play with.
Go here: http://help.mojang.com/ It seems that multi player sessions are offline. Hopefully Mojang fix it soon...... At least we know what is happening.
A suggestion to blackie:
for the website you should have a shoutbox. I don't know how to get them but I've seen them on other websites. they help if you want help from a mod or someone who's online.
Is the whole(or almost whole) error ......ver returned HTTP response code: 503 for URL: http://session.minecraft.net/game/joinserver.jsp?user=(your username)&sessionId=8633.....? some bits might be different but i'm getting it too. I was looking forward to joining a tekkit server and this one looks like a really good one. Can anyone help us?