1. Yes indeed - you can amass quite a fleet, in fact. There are various capital ships, some mercantile, some combat, and a few with more or less hybrid function.
2. Sadly, no. The other ships you get have preset weapon loadouts - you have the option to only partially (or not at all) fill various shield and weapon slots, bur except in situations of extreme poverty, there's absolutely no reason to do so. You get to equip very scalable numbers of drones aboard your ships, but alas they are of dubious value (the combat ones, at any rate - the economic ones work fine and are crucial)
3. SETA is craftable from 4 inventory items, and there's no required time-stamp or mission to do so - it's available from start (but the different pieces' probability distribution is not geographically uniform - ie. the different pieces all have particular systems they're most likely to drop in) The JumpDrive is a relatively late-game thing - in fact, in a campaign game the mission (unlike SETA, there is a set of missions for this) only appears once the main plot is completed, and it requires considerable collecting of rare drops. The personal JumpDrive is a VERY powerful means of travel. However, there is another way to avoid highways (I personally more or less detest them, myself) - hitch a ride on a capital ship (that you own.) Simply dock at one of your capital ships and order the ship captain to take you somewhere. Here tastes/needs differ - some players mostly get around on a freighter, overseeing that ship's trading, some players prefer a small and agile combat frigate to get around in, some players don't mind slower travel in favour of flying around on their flagship - most players do more than one of these during the course of a game.
4. PMC hostility is part of the plot (a bit like having Liberty gunning for you back in Freelancer). The obstacles this poses are merely part of the challenge. Note the dollowing: PMC will attack your COMBAT assets on sight, but will leave your civilian assets alone - thus, your capital freighters, miners, and builders can operate quite freely (though, of course, they still can't dock at PMC stations.) You can also move undisturbed through PMC-policed space if you travel aboard a freighter.
5. Your Rahanas capital freighter (and any other assets) do vanish at that point in the game, as they were "confiscated by PMC".
You will get that ship, and anything else you may have had confiscated, a bit later in the campaign. TIP: When you do, do yourself a favour and check that the ship's engineer is in "Repair" mode, instead of "None" - this will almost certainly be the case, it's a known bug. To fix, simply dock to that ship, recall that engineer, then assign him/her again.
ADDITIONAL: Here's an important piece of advice for any Egosoft space game: take your time in the campaign, don't rush it, don't feel bullied into following the mission marker. The objectives are virtually never time limited, so go ahead and build up your economy between missions - this will stand you in good stead later down the line, both for the campaign, and for the post-campaign sandbox.
Good hunting!
