It sounds like you have several things going on at once. There may be two different issues with the warning lights, or it could all be related. When they all come on at once like that, it usually indicates an electrical problem, such as a weak battery, corroded connections, or a failing alternator, (which could be as simple as worn out brushes) rather than a problem with the various systems the lights are warning about (it's very unlikely that ALL of those components would have a problem at the same time) Since it happened when you went around a turn, that would seem to suggest a wire that is making intermittent contact. The oil light coming on could well be related to this as well, or it could have a wiring problem of its own, a bad sensor, or the car could have been low on oil. Even without tools or experience, you should be able to tell if the engine has any serious oil leaks. It's not uncommon for there to be a little oil here and there, but if its all over the place, and dripping on the ground, you have a problem. Also, you don't want to use oil any thinner than 10W30 (such as 5W or 0W anything) if you do, you may not have enough oil pressure. Assuming you have suitable oil in the engine, it is unlikely that it is so worn out that there is no oil pressure----209K miles is middle age for a Volvo. The tach jumping around is either another bad connection, low battery/alternator voltage, or perhaps a failing crankshaft position sensor. If the engine doesn't hiccup when the tach jumps, but keeps running smoothly, it's probably not the sensor. The brakes squeaking may be perfectly normal (though annoying) or it could indicate worn out pads. Shaking at 55 is probably a wheel that is out of balance, or a tire that is worn unevenly so that it is no longer perfectly round.

While it's unfortunate that you have had so many problems crop up right off the bat, it doesn't mean you should give up on the car, as it is ideally suited for your needs. Some friends of mine, also musicians, have an 89 740 wagon, which now has about 370K miles on it, and its still going strong. They love it, as it is the only car they have ever had that can carry three musicians and all their equipment, even when one of them plays the bass fiddle. You should put some time and effort into diagnosing/fixing your car's problems, after which there is a good chance it will serve you well for years to come.

See the 700/900 FAQ on this site for a huge amount of information on these cars---better than any of the available shop manuals.