I have a Tif419 Bermuda lawn. Total lawn area is 30,000 sq ft. I'm considering selling my riding mower and getting a 5 gang reel mower to pull behind my side by side. Anybody familiar with them?

Pull behind would be difficult unless you have a wide-open space. I would look for a used golf course trim mower - riding, 3 reels, about 6' cut.
Where are you located?

I'm in Rockwall. My actual Tif419 lawn is 30,000 sq ft but I also have another acre that is just native grass/weeds. I was looking to go the pull behind reel because my gate to my back yard is 5 ft wide, which the folded up gang reel and my side by side would fit through. It's not like my zero turn takes a crazy long time to mow, about 2 hours, with mow, trim, edge, and blower. I just feel like the wider swath of the reel mower would get it done quicker and look better in the end. I do have wide open space. 3 trees in the front on 15,000 sq ft, 3 trees in the back on 15,000 sq ft, and the rest is wide open. I have my push behind mower for the spaces I cant get.

Do you know how to back-lap?

As someone with over a decade of experience maintaining golf courses and reel mowers, Don't do it. The maintenance is a nightmare and if you have any weeds you will be pissed when the reel mower just lays them over.