The above are great suggestions. When it comes to socket sets, watch for a sale on Sears Craftsman sets. They work well and are reasonably priced (particularly when on sale). After the basic metric set (sockets, extensions, handles), I would purchase a few deep sockets. They are more useful to me than pass-through sockets. You don't need every size - 10mm, 12mm and 14mm will handle most needs - get other deep sockets strictly as needed. Add in a 1/2" drive breaker bar plus a long pipe cheater.
Here's a serious cheater in use, about to loosen a strut bolt. Note the impact socket in use:
As you need additional sockets, get them individually. For example, if you plan to do a strut job, you need an impact socket to get the nuts off - the nuts are that tight. No, you don't need an impact wrench - only the socket. Impact sockets have very thick walls and are very strong. You'll put enough force on things doing a strut job to crack a regular socket (ask me how I know).
You might also get an impact socket to remove the front motor mount nuts. . . because the nuts used by Subaru are too soft, and a regular socket will will flex and tend to round them off. The forces aren't that great. . . but the nuts are cr*p.
Get metric sets of open-end wrenches and box-end wrenches. Crafstman are fine, but other brands are good, too. For hand tools, I would generally avoid Harbor Freight. It's no fun having a wrench or socket snap when you putting the muscle to it. Even with good tools, an occasional failure is going to happen.
Jacks? I have a floor jack but rarely use it. I like low ramps instead. Make yourself a set out of 1x6's or 2x6's or something similar. For many operations (e.g. oil changes), you need to reach
under the vehicle . . . but not crawl
under. Low ramps are very handy for this.
I had a set of car stands but rarely used them. They started rusting so I passed them on to a relative (who I do not like). Back at home, a simple way to support a raised vehicle is to use short sections of 4x4 post. 12" sections are fine, but the length is not critical. In the following picture, the vehicle was raised using the on-vehicle jack, then supported by 4x4 blocks. BTW, Lowes or Home Depot will cut a 4x4 post however you want it (e.g. 12" sections).
Your on-vehicle jack is very handy. I've got an extra one (not sure where it came from - maybe left-overs from a Toyota that was totaled or ??). You might try the on-vehicle jack before springing for a floor jack. Either way, if you plan to crawl under the vehicle, you need to support it properly (or be sure your life insurance is paid up).
One more thing you might find handy: Get a 16" piece of 1/2" iron pipe - either galvanized or black is fine. Store this in your vehicle trunk for roadside emergencies - as a cheater for your on-vehicle lug wrench. The on-vehicle lug wrench is handy and the wrench socket end fits the lug nuts properly. But the handle is very short. . . and this cheater pipe is the 'fix'. I usually use this wrench/cheater combo when working on tires in the garage.