Usually these posts start with "I ran a 18min 5K in high school but now I'm in my late 30s, smoke and drink too much, and I'm wheel chair bound. Also, my wife just gave birth to our third set of twins. Can I BQ this weekend?" But you actually have a pretty good shot given your PRs on relatively low mileage and a full year to train. Honestly, you could prob run a BQ a whole lot sooner.
Hire a coach? Not a bad idea but probably not necessary. I have used two coaches. The first was online and sent me fairly generic training plans (plagiarized versions of Hansen's 5k plan I later found out) and we exchanged a few emails. Pretty much worthless for the money I spent ($100 up front, $45/month) and I cut my losses after 3 months. The next guy was a coach at a track club. It was $15/session and there were four sessions a week. He was better because he actually saw me run and gave me some help with my form, pacing, and race strategy. There were about 50 people at each session of all ability groups (from 15:00 5K guys to walkers) so there wasn't a whole lot of individual attention. Still, it was worth it just for the fact that I got to work out with some faster runners. I think joining a local running club would be a good idea to find some similarly paced runners that you can train with.
Free Plan? Yeah, there are some decent free plans out there. That is a viable course of action. You can actually find Pfitz 18/70 Marathon plan online for free and a whole of people have had success with that plan. I think you are better off just forking over $25 for Pfitz Advanced Marathoning or Daniels Running Formula. Those books cover nutrition, cross training, race prep, etc.
Generally speaking, I would say you need to slowly build up your mileage over the next few months to around 50 - 70 MPW. 50 MPW seems to be the minimum and most people need around 70 MPW to go sub3. Once you are comfortable at the higher mileage start Daniels, Pfitz, or any other reputable training plan. Anecdotally, I jumped into Pfitz 12/70 off 3 months of 50-60 MPW base training and ran 2:51 for my only marathon. I haven't used Daniels but my understanding is that you need to be more comfortable at higher mileage before starting... he hits jumps into it a bit quick whereas Pfitz has a few weeks in the 50s up front.
You will have no problem running sub3.