Hiya Arallera!
I’m an officer in the Guild Shred Lobster, and I think you might be a good fit with us! I’ll do a copy and paste thing of our recruiting post, so you can take a look and see if we might be a good fit for you.
We’re not heading towards mythic raiding, but are striving for AOTC. We also like to run Mythic + dungeons, which we can help you get familiar with if that sounds foreign to you as a returning player. 
As far as what spec/class to play, we always encourage folks to play what they enjoy the most. At the end of the day, we’re here to have fun and enjoy the game together (and hopefully get some sweet lootz in the process lol ). As far as raiding goes, we’re mainly looking for DPS, but having a toon that you’re comfortable switching rolls on, is always nice to have in our back pocket if necessary.
Anyway, thanks for your time and here’s that link to our recruitment post. My contact info is listed towards the bottom (I go by Malo in game). Have a good one!