Yeah. I had quite a bit of Linux experience before I got my LPI, so it would be a good idea to install a test server with centos or debian and play around. Or, at the very least, install something in vmware.
All 3 of the comptia tends to go for competence moreso than administration certification, so you may not need it. I myself haven't gotten any of those 3 listed exams (although at one point I was studying for the Network+, I just never got around to finishing it). Whether or not you need a class really depends on how comfortable you feel. I picked up a Net+ Exam Prep book for like $30. Read the book twice, take a few practice exams, and see if you feel comfortable.
wk: nah, I haven't really gotten any certs outside of my LPI (lpi.org). Right now I'm kinda swamped with work, but my next goals are my mysql dba (which shouldn't take more than a month, I have a book and feel I pretty much know everything, so I just need a refresher), then RHCE (redhat), then I want to start going for my net+ and ccna. I think I can get my mysql dba and rhce this year, the ccna is more of a long term goal.