I'm considering switching to active. Will I have to take a rank reduction as an 0-2?

I just switched over to the Regular Army. You won't lose any rank but they will have to determine your Year Group. That will determine your promotions for the future. I lost some time due to this. HRC will calculate this. It is a pretty simple process. It just takes a good bit of time. If you have any questions just let me know.

No, the issue is getting past the Call to active duty program, they are tough and only select the best candidates, it's not like the enlisted side where you can choose to go active the CALL program is tough and only accept the most qualified candidates, it also takes a long time for the entire process.
Get your packet ready and have some excellent letters of recommendation in advance. Good luck!

Not at all. As a Commissioned Officer it's EXTREMELY uncommon to require an administrative rank reduction when changing branch status. However, the challenge you will encounter is trying to acquire approval to switch to Active Duty in the first place. It's a long tough process if you can even get accepted; and usually you have to be in some type of specialty branch (ie. Medical, JAG, Nuclear Science...). Last I heard, Active Duty was only taking transfers from the Guard under very special circumstances. Unfortunately, it may come down to waiting for another Global conflict before those "flood gates" open again. Look into it anyway, but don't be surprised if you are shut down quickly.