Pressure relief:
Usually if it sits long enough the pressure will bleed down by itself, however, if it doesn't or you don't want to wait, you can crack loose the regulator nut where it tightens to the rail. Go slow, and wrap a rag as it'll spew a bit if there's any real pressure.
Rail:
If you're going to replace the short lines between rail and injectors, then all you need do is unhook the regulator, the feed line and the support bolt that's in the middle of the rail. Cut the short lines in the middle and the one that feeds the cold start injector (Motronic has one of those, right?) then pull the rail off.
Even though the book says to cut those little washer thingies on the ends of the short hoses, don't, use a soldering iron to cut/peel the rubber away and save the washers as you can re-use them with the new line (provided you get the correct size, otherwise you'll have to get fuel injection specific hose clamps and not use the washer bits)
The stripped allen head:
You mean the threads or the head?
If the threads, you're in for some work, up to and including either helicoil or having it welded up then re-drilled and tapped.
If it's the socket where the wrench goes, then you might be able to get ahold of it using needle nose vice grips (it's not in there stupid tight) and back it out so you can replace it with a new one. (common size found in most hardware store bolt bins. Take the old one for size and length reference)
Reinstall the rail:
Get all the short hoses onto the injectors first with either the washer thingies or the hose clamps holding then on, then just kinda line up all of those with the nipples on the rail and push it into place. Reinstall the regulator, put a fresh line on the cold start valve, hook up the feed line, re-do the support bolt and fire it up while looking closely for leaks.
That should cover most all of it, and if not mabe someone will trip in and offer some more finite points.