Pinterest algo is, let's say weird. If your pin is good one (gets a lot of repins and likes), it doesn't only reach your followers, they will also show it to users that aren't following your account but are interested in that kind of content.
I can't give you exact number but CTR on pins is much higher than on Facebook, because you don't get much from pin itself unless it's infographic and there's no "real life friends" there with pics of their kids to restrains you from clicking useful links
Maybe I have something about "quotes", but unfortunately, that giveaway is closed for now. To join groups, you can comment on pins of board owners asking nicely to add you. Just make sure your profile looks good (not spammy).
Feel free to use new accounts, but create boards on them, add profile pic, some bio, make them look real and you won't have issues. Of course, I'll repeat for 100th time, don't repin only pins from your website. Mix it, mix it a lot!