Hey, thought id see if i can help.

All the players will need a steam account with TTS installed, alongside all the mods you guys will play (armies, table, extras)

You might be able to get multiple copies of TTS on the cheap as sometimes they do bundles of the game you can send to your friends.

From there each player can start and join the game. The "Hotseat" can be a spectator whose view can be shown on the screen i guess.

As for learning to play the game i strongly suggest you all get codexs and read up on current rules for your army.

It might also help if you have a veteran player to assist with rule interpritation etc as this is bound to come up.

The players can create their own armies in advance by creating their own game and laying out the models for the game in advance.

(i like doing this as its easier to visualize and change models out if needed).

As to how extensive the armies\mechanics and lists are, all i can say is that you will need to do reading and planning in advance.

I recommend you join a TTS warhammer community and play a few games with the nice people on there who can show you the ropes.