I’ve moved 1000 miles from my unit due to civilian employment. Is the IRR an option for me if there are no vacancies for 25C?

You can put in an IRR packet, however you should work with your existing unit's Company Commander and Unit Administrator (UA) to RST fro Drill with a local unit in your area. Then contact a local recruiter who can scan available vacancies for units near your HOR.

Then have your losing unit initiate the Form 4651 to transfer to another unit. Since you are a junior Soldier, pretty much any unit you join will be a "will train" unit & you could probably reclassify into another MOS should you choose to. Make sure you're not under any MOS-specific bonuses or special pays or you may have to pay these payments back.

It is an option, but not the first one. If you are on your initial enlistment you owe 8 total years, and yes, that can include the IRR, but you are also a PFC, and reserve units are authorized to go over 100% on E4 and below, so any kind of unit can take you as excess in 25C if there are no vacancies.
That said, you could also take this opportunity to get a reclass school like 25B or 17 series, something that is more useful later on in the civilian job market.

The IRR would be a viable option. However, there's also the option to re-class to a different MOS with a nearby unit. Keep in mind that you get no retirement points for being in the IRR.