Hi! 
I only started RP'ing (never had RP'ed before in my life) five months ago, I'll share what I know from noob-to-noob and the things I've picked-up on, hehe.
By RP group do you mean a posse of RP'ers who are involved with your storyline? Get a group of friends, browse people's profiles who interest you (here!! http://www.ffxiv-roleplayers.com/wiki/ ) and message them asking if there's anything you could work out - most I've found are looking for childhood friends, family members, stuff like that and they're usually very friendly and nice about it! Or join a Free Company (Guild.)
Character progression is up to you, but... like I re-made my character's personality three times over the course of the months :/ S'been quite a battle. The more I thought about how my character acted; how her background and storyline affected her as a person now, the more I had to change how she acted outwardly towards others. I find in the early stages there's not too much wrong with playing about and changing their personality, but create a foundation first to help yourself so you don't risk changing too much. Get a character background basis sorted out, and what kinda personality you'd like to play.Â
Leave things vague! If you're unsure with how exactly you want to play out things, leave it vague!Â
Example: my character is a country bumpkin, and was from random make-believe village land, until I got to talk about with some well-knowledgeable people about in-game locations and now I was able to choose where she's from that made sense in my head, and for my character. Another example is that I left her family vague, and was able to incorporate a lovely lady into my storyline as her sister!
Oh! Also! If you mean character progression as well with her own battles in-life, like an event that made her re-think life, or want to grow stronger as a person, make a post about it in the forums asking for help/people to help RP as the background characters, or PM people as well!
Anytime is acceptable for OOC should it call for it! Most people surround their messages ((like this)) to show that they're speaking OOC - to show that they're correcting a typo they've made or need to go. Though, I personally don't use brackets much because I always type in quotation marks if I'm RP'ing, and I chat to non-RP'ers as well.
Powerful? I think... from what I was told, say your character is an elite soldier, and should be able to beat-up a squire (I haven't RP'ed fighting yet at all) I'm told everything is handled by roll, so should the squire get a better roll he'll get a 'lucky shot.' But as far as in-general goes, if you're God-moding it's a no-no where you can automatically beat everybody up and/or kill them or decide their fates.Â
(Or Super Saiyan, super-duper-amazing-powers that shouldn't exist like magical princess from the planet of unicorns.)
Why couldn't you use your character for OOC? You don't need to stay in IC all the time I'm a PVE'er foremost, and I have two characters: I made this one solely for RP, but then I started grinding her in dungeons because the gear's toooo preetttyy. There is a problem sometimes where you're not in IC gear and people try to RP thinking you're in canon-gear, but I just politely whisper and tell them I'm not, and then do ninja-clothes-changing-jutsu and resume to do RP with them (if I'm in the mood.)
[EDIT] I Edited my post like five gazillion times <_< Kept having more to say. Hope I helped.
I only started RP'ing (never had RP'ed before in my life) five months ago, I'll share what I know from noob-to-noob and the things I've picked-up on, hehe.
By RP group do you mean a posse of RP'ers who are involved with your storyline? Get a group of friends, browse people's profiles who interest you (here!! http://www.ffxiv-roleplayers.com/wiki/ ) and message them asking if there's anything you could work out - most I've found are looking for childhood friends, family members, stuff like that and they're usually very friendly and nice about it! Or join a Free Company (Guild.)
Character progression is up to you, but... like I re-made my character's personality three times over the course of the months :/ S'been quite a battle. The more I thought about how my character acted; how her background and storyline affected her as a person now, the more I had to change how she acted outwardly towards others. I find in the early stages there's not too much wrong with playing about and changing their personality, but create a foundation first to help yourself so you don't risk changing too much. Get a character background basis sorted out, and what kinda personality you'd like to play.Â
Leave things vague! If you're unsure with how exactly you want to play out things, leave it vague!Â
Example: my character is a country bumpkin, and was from random make-believe village land, until I got to talk about with some well-knowledgeable people about in-game locations and now I was able to choose where she's from that made sense in my head, and for my character. Another example is that I left her family vague, and was able to incorporate a lovely lady into my storyline as her sister!
Oh! Also! If you mean character progression as well with her own battles in-life, like an event that made her re-think life, or want to grow stronger as a person, make a post about it in the forums asking for help/people to help RP as the background characters, or PM people as well!
Anytime is acceptable for OOC should it call for it! Most people surround their messages ((like this)) to show that they're speaking OOC - to show that they're correcting a typo they've made or need to go. Though, I personally don't use brackets much because I always type in quotation marks if I'm RP'ing, and I chat to non-RP'ers as well.
Powerful? I think... from what I was told, say your character is an elite soldier, and should be able to beat-up a squire (I haven't RP'ed fighting yet at all) I'm told everything is handled by roll, so should the squire get a better roll he'll get a 'lucky shot.' But as far as in-general goes, if you're God-moding it's a no-no where you can automatically beat everybody up and/or kill them or decide their fates.Â
(Or Super Saiyan, super-duper-amazing-powers that shouldn't exist like magical princess from the planet of unicorns.)
Why couldn't you use your character for OOC? You don't need to stay in IC all the time
 I'm a PVE'er foremost, and I have two characters: I made this one solely for RP, but then I started grinding her in dungeons because the gear's toooo preetttyy. There is a problem sometimes where you're not in IC gear and people try to RP thinking you're in canon-gear, but I just politely whisper and tell them I'm not, and then do ninja-clothes-changing-jutsu and resume to do RP with them (if I'm in the mood.)[EDIT] I Edited my post like five gazillion times <_< Kept having more to say. Hope I helped.
