This is your thread- Don't apologize for questions. Let me try to help- I'm old enough to remember when Sei owned the site originally, so I may be of some assistance.
What sort of changes will there be?
We have no idea. The member base has been kept in the dark- The suspense is there, but no real teasers as of yet. As of now, only one thing has been dropped to hint us as to what is coming.
https://www.fairytailrp.com/t40305-the-dragon-emperor-quest-ongoingNow, this isn't much to go on. However- Never have I seen the site offer something like this, neither with Shinsei (the current owner, going by Jyu) nor Xun (the last owner, who was likely in charge when you first joined). So we can assume that this time around will allow people who enjoy Combat RP to partake in combat RP, it will likely force people with limited magics (Such as Dragon Slayer) to stay active, and it seems like there WILL be player driven plot. Cool right?
Will everyone have to start their characters again?
Luckily, we DO have an answer for this one. People will be able to recreate their characters on here- However, they will not have any plot buildup like they did prior. It is essentially a fresh start. In fact, the only people who seem to be getting anything off the bat are people with specific Post Counts. While I do not know what the cutoff for C rank is, it seems like people with 2000+ posts are getting to start as B rank. So yes, you will have to start your character again. But so will everyone! And trust me- Combat is not specifically about power. Hell, this site won't even be specifically about combat- That's not Sei's style. So don't worry!
I think I'd like to change a few things, but if I remember correctly there are things I'd like to keep from my current / last character.
Not a question per-se, but still deserves an answer. You will be submitting a new character app. While this hasn't been confirmed, there were NO apps transferred over, and he made sure to clear EVERYTHING out of public view. Now, if I know Sei (which I do), I highly doubt he's going to just put the profiles back. If he's gone through the trouble of bringing the site back into a "Development" state, then EVERYTHING will be new. So don't worry, you'll be able to make your character- Probably however you like. The only limitations I can think of will be Limited Magics, but that's literally any fairy tail site.
Once again- This is all speculation. He hasn't been too open with information, and we don't even know who his Development team is (or if he really even has one?) But this should still help, and all the speculation is with reason. I hope this helped, and welcome back!