I looked around and couldn't find anything on this so I apologize in advance if this has been mentioned. I just started RTK and before I did that I've been studying kanji on wanikani.com where you learn Kanji+readings you also learn vocab. I was thinking about doing RTK along with that website. My question is, is that counter productive or should I just go for it?

The fastest way is to do RTK and then learn vocab through sentences/anki decks.

I would either focus on your current way, or focus on the RTK way. If you do RTK though you don't have to lose what you learned; you can keep reviewing it just don't learn anything else via that method, because ideally whatever method you commit to you want to finish as fast as possible.

I 'finished' RTK. That being said I'm ofrgetting characters here and there quite often so I review as much as I can. But I also got beta access to WaniKani and I'm doing that at the moment. It's a good website and I wouldn't assume it'd make RTK any harder to complete since the workload in WaniKani is very low and it's a slow method. I do like it though.