Please keep your cat indoors. Even if you are in a rural area, it is very dangerous as you found out. Especially when they are so young. Also, she can get pregnant in just a few months. She can be spayed once she reaches 2 pounds.
Please also do not consider declawing your kitty. There are a plethora of reasons why but you can look up declaw on this site and find plenty of information.
The easiest way to trim a kitten's claws is to wait until she is nice and sleepy, then carefully trim just the tips off. You can see the quick through the claws and make sure to avoid that. Sometimes they get squirmy, so be persistant and wait until she's sleepy again, then trim a couple more.
Get a few scratching posts, both vertical and horizontal for her to learn proper scratching behavior. You don't want her to practice on your couch.
Since you are new to cats but not to dogs, please understand that behavior training is very different in the two species. Cats do not respond well to negative reinforcement like scolding, spanking or rubbing their nose in an accident. Try things like distraction and redirection. If she's doing something you don't want her to do, distract her with a toy and redirect her energy into something positive.
If you want her to be able to experience the great outdoors, start training her now with a harness and leash so you can take her out on supervised visits. You could also consider a cat enclosure that would keep her safe and give her somewhere to play and relax in the outdoors.
Congratulations on your new kitty and condolences for poor Sebastian.