As someone who frequently roleplays on Discord in tabletop groups and has done other RPs on Discord, it's alright for quick bursts. If you want to post like you do on the forum, perhaps it'd be better to stay on the forum or in PMs if in the case of a PM RP because the 2K character limit is annoying for RP.

Regarding it being used alongside the site, I like using it. You'll generally find your partners online on Discord more than you would find them on RPG at least in my experience, so you can quickly hit them up and ask for posts or whatever. The price you pay, however, is your OOC being practically dead since OOC chatter would mainly happen on Discord.