This comment is not intended to offend, but to give you a realistic answer before you "get too excited" about the idea.

Advertising agencies, at least any half-way decent agency, are extremely competitive to break into. Yes, people already within the industry move around and change employers alllll the time, but to break-in is a completely different story. If you want to stay in a smaller town, it may be easier to break in. Most people in advertising/marketing have those positions coming straight out of undergrad or grad school.

Based off wanting "a combination of teamwork and solitary work", this already seems like a bad fit for you. There will be some days where you'll get the luxury of 2 hours by yourself to write a creative brief, emails, etc...but 99% of the time you'll be answering calls, reviewing projects with your team, and sucking up to your manager. You will get slightly more "alone time" as a creative person.

Truthfully, I don't even know where you could fit in... POSSIBLY a Jr. level producer with your video background, but that really depends on if the job you have now is applicable. Another comment mentioned the multi-media dept. That's your best bet in my mind. You probably wouldn't get any account management type role as you've already been working for 5+ years with what seems like irrelevant experience. You do seem to have technical skill, but if you want to be a "Creative", you'd definitely have to put together a portfolio of creative spec ads. If you don't even know what that entails or where to start, I would begin looking that up ASAP. Begin learning the Adobe creative suite and researching portfiolio schools. Chicago Portfolio School, Miami Ad School, Creative Circus, VCU Brandcenter...to name some notable ones.