This all sounds very familiar as I'm of limited mechanical abilities, though feel I can think my way through many problems. I generally find most jobs are much quicker the second time around. A few tips I seem to have picked up from my own mechanical mentors over the last 8 years of DIY are:
Sometimes I tackle jobs succesfully, but more often I tackle things that should take an hour, spend all day, don't fix the problem, and cause one or two new ones into the bargain.
(1) Research the job thoroughly first and prepare for it. Anticipate the possible problems and eliminate them before starting on the job proper.
If the job needs you to undo things that haven't undone in a long time then apply loosening juice beforehand over period of days or even weeks. Don't expect brake bleed nipples to undo without pre-persuasion. Heat can be very useful for persuasion too.
(2) Stick to the job you've started to do: it's probably the most urgent one, and the other jobs you see along the way can be kept for another time, unless positively dangerous.
(3) For hydropneumatic Citroens, certain tools are essential or can at least make the job much quicker and more convenient. In this class I'd include a sphere tool (you're welcome to borrow mine, Sam), strong ring spanners with hex heads in 8 and 10mm (the basic sizes) for hydraulic junctions and cut-out to allow use on pipes. A good quality 12mm open spanner is essential for releasing system pressure at the Pressure regulator prior to hydraulic work. Internal trim on later cars is held on almost exclusively by torx head screws.
(4) If what you're doing isn't working, stop and think. Normally you need one of two things : (i) a bit more grunt (ii) a bit more guile. The skill is in working out which is the appropriate one....
(5) Almost any bit of trim held on by a nut or bolt on a Citroen BX can be removed with an 8mm,10mm and 13mm spanner.