If you are handy with tools and can pay attention to instructions (and have the proper tools) you can do the struts, and starter yourself. Probably the engine mounts too, but you may want to pay (SOMEBODY ELSE) to do that. Like /u/OM617 said, no mechanic would suggest replacing one shock/strut. That is dumb.
You can get shocks struts and springs from IPD for under 800 bucks and do it yourself. (I have over 5k of performance/replacement parts from this website in 2 different cars and have used them since the 90s)
I have had 3 different Volvos in the 1997-1998 range.
They have heater issues. I would get your coolant flushed, and then check the connections to your heater core. They are behind the engine, and have yellow couplings leading into the firewall.
You say you have a PUDDLE under your car? You sure it's oil? If you have a puddle after work most days, it isn't oil, it's coolant. You probably have cracked coolant hoses/bad heatercore/bad couplings.
The heatercore and couplings are relatively easy to do yourself, I can provide some good guides online. It's just a pain in the ass and you have to play Twister with your car to get to certain areas.
If you want to own this car, and you want to work on it yourself. Buy these tools, and buy QUALITY tools. Affordable quality can be found at O Reilly's/Autozone. [This is the brand]d(http://www.oreillyauto.com/site/c/detail/PTT0/GM8761/N0761.oap?ck=Search_N0761_-1_-1&pt=N0761&ppt=C0185) I use for my hand tools and I have found the quality to be on par or better than SEARS bought Craftsman. Don't buy the cheapest versions.
A torx set (quality, not cheap, cheap torx will turn into butter under stress)
An E5 External Torx.
Multiple socket wrenches of various sizes with extensions.
A Metric socket set with at least 5mm-19mm
DEEP Sockets for 14mm, 19mm, and 22mm.
A FLOOR jack. A big one. 4 jackstands.
A medium and long flat head screwdriver (spend more on these)
A medium and long phillips head screwdriver (spend more on these)
A good working light you can have under the car with you. I prefer headlamps.
A GOOD pair of vice grips, large and medium. I like HUSKY brand, which sounds cheap but is better than VISE GRIP brand in my opinion.
Dewalt, Milwaukee, HUSKY are good brands.