
Welcome to HLP!
The exits are randomly located throughout the station, but they are so rarely used that I doubt you could use them even if you wanted. Once you get in, there's no easy way out. Air ducts are one remote possibility, but the problem is that our resident Shivan, Carl, lives there, which makes air duct expeditions extremely dangerous. Should you, however, encounter Carl, make sure you give him your lunch and he might let you live.
Plasma rifles would be extremely useful and we actually have plentiful of them, but they are in lockers here and there and they can only be opened by

or a hyperintelligent shade of blue, both of which have not been seen in the Freespace universe in a while. Actually, the closest thing to a hyperintelligent shade of blue we have is a being known as Transcend, but It has been very difficult to communicate with him.
Enjoy your stay at HLP.
AS for the questions:
1. Of course it is. Go ahead.

The trouble is to find enough people who wish to play multiplayer. FS has always been very single-player-oriented game (in a good way).
2. You have to find the maps from the VP files using VPView (for example). Then you can edit the texture and place the edited texture in C:\Your\Freespace\Path\Shivan_Ulysses\data\maps\
Then you open the Launcher, choose your mod to be "Shivan_Ulysses", and it should show the edited map.
You can use at least *.dds, *.pcx and *.dds files as texture maps. Perhaps the game can use others too, but dds is the best and I suggest you use it in your modifications. You need, for example, GIMP and the DDS Plugin for that. I trust you can seek these tools for yourself...
3. I have no idea.

4. I don't know of any. Though you will undoubtedly get tons of visits from Google, as people are looking information about the infamous StarForce(tm)... I would suggest changing the name of the page if it's in any way possible. StarForce brings so much *not nice* things onto mind...

5. I can't model, I wouldn't know.

And IMO, if your page is Freespace oriented (as it seems to be), of course you should have both HLP and SCP pages on link list.
PS. If you plan to have a multiplayer squadron,
don't call it Star Force Squadron...