So every forum on the internet told me to have a professional fix my issue, everyone I asked in person suggested I pay to have it fixed. As usual, my stubbornness forced me to give it a try; it turned out pretty ok to me!
When I first saw the hole I was pretty disappointed that I missed it in my initial inspection, I thought that it was rusted through.

Once I started cutting away at it I was really relieved that it WASN'T completely rusted away. Metal behind there was pretty solid minus some of the divots in the next picture.

All cleaned up! Not sure why the dark spots are like that but I went through a half a dozen dremels making sure there were no more rusty spots!

After a little welding and a little grinding, I'm all done. I know I'm not the best welder and it's honestly been awhile since I've done any welding but I think that it'll restore the previous strength and repair the damage that was done.

Looks good! From the title I was expecting a story of paying a professional gone wrong...
In reply to GameboyRMH:
My first thought was hiring a professional could only have a happy ending but then I thought of the "He almost got me until I looked a little closer" thread.
Looks pretty good! I'd be a little too wimpy and have paid, but metal is metal and melts at the appropriate temperature whether it's building a gate or welding a car frame. Well, that and only 1 in 7 or 10 of my welds come out good, so....
Kudos, and good on ya!
Looks good from my side of the interweb 
oldtin
PowerDork
3/17/17 4:40 p.m.
looking good - surprising that's about the only hole on the opel
i thought there was none, body was incredibly clean, everything seemed in order, started right up from a cold start.
finally ordered all of the absolutely necessary stuff 384 euro later... now i wait for an order confirmation and the bill. should be ready for inspection soon!