Welcome at Go and OGS.
If you find the time settings of open challenges too fast, I’d recommend creating a “custom challenge” with more fitting time settings. (Avoid “simple” time settings, they have many bugs).
The OpenStudyGroup (OSR) is a place you can find players to play games on a slow pass (30m+overtime on 19x19), and the possibility to get a review or some general tips afterwards.
At beginner level, your opponent won’t have a big advantage by trying to play joseki sequences, as you probably won’t follow up with a move that’s in the joseki library. Your opponent then is left on his own.
There are a hand full of short sequences, that are helpful to know after you learned the basics of the game, but at DDK (double digit Kyu) level, the use of Joseki libraries is very uncommon. (More than half of the OGS player base is DDK by the way).
On a funny note