Hey there! Welcome to WaniKani, I’m glad you’re enjoying it!
Yeah, Duolingo for Japanese is not . . . . ideal. Not the worst, but not the best either. If you want to find other materials to study from, I’d suggest taking a look around the Japanese resources section of the forums here as there’s some good recommendations. I personally have used Genki and am using Kanzen Master to study for the JLPT, but there’s lots of other ones that fit different learning styles.
Don’t worry about your speed if it’s causing you stress! Learning is the important thing here, and sometimes a bit slower is better. Find your optimal speed and I’m sure you’ll be fine 
If you have any questions or problems or anything, don’t hesitate to hit up the forums! We’re all pretty nice here, and I’ve found it to be a super helpful and supportive community.
Best of luck on your kanji/Japanese adventure! がんばりましょう！