Disclaimer, I have very little experience, but I'll try to help.
Good.
You will have to be hired by the ANG or Reserve unit of which you would like to be employed by. Already having a pilot slot may help, but it may not. That specific unit is going to hire you based off of a variety of things not just the fact that you already have a pilot slot via ROTC.
Really? There's plenty good info on the 2 pages of this thread prior to you posting. And has been discussed elsewhere on this board. This is a choice you will be making. That choice is 100% subjective. No one can tell you which one is better for you specifically. That's for you to find out.
If you really decide the Guard is for you than why be intimidated? It will certainly be a lot of work finding a unit, getting hired, etc. but if that's where you decided you want to be than go for it. But you're turning down a slot on active duty (if you decide to go guard) a slot that once turned down you can never be accepted for again. I went through the whole thinking about transferring to the Guard prior to my commissioning as well, but it turned out that once I dug up info on what the Guard is like I found out that the grass isn't always greener on the other side. I'm not trying to influence you one way or the other. But the way I figure is that you have a UPT slot (possibly an ENJJPT slot), an FC1 and a commission into AD if you so desire it. Going to the other side of the house, which I'm sure certainly has it's advantages, means giving up all that you have already worked for an obtained (at least temporarily).
Another thing to think about is that you may believe that you will really enjoy a specific airframe and how it'd be nice to know where you'll end up after UPT. While all your bros get the opportunity to change their mind, talk to IPs who have various backgrounds, and see which communities they might want to end up in. Most people go in wanting a specific airframe, then within days/weeks/months suddenly aren't as picky.
Best of luck.