Hi Sherry,
Here's an idea that might come in handy... As a past contractor, I'm also a driven DIYer, and have found a middle-road that works for me. Have a few contractors/ installers out to look at your deck project, with the finish/es your considering. Share with them your & your husband's desire to be a part of the process & a bit about your backgrounds in working with concrete/ coatings/ etc. They may be willing to offer a break if your work alongside their crew actually saves them time/ labor. I've done this with several projects which involved contractors, and never had a problem with it- This is most often a "fit" for smaller companies that know they're backlogged, and appreciate a qualified homeowner who's willing to help. The crew saved some man-hours to tend to other jobs, and I got be a part of the process while saving a share of the cost- a Win-Win. Meanwhile, you still get a professional product with warranties intact.

Last thing: There are a few forums online with "horror stories" about DIY concrete & epoxy jobs. They're exactly like the "Algae Crisis" posts here, except about a material that's built to last for decades!! I'm not trying to discourage you- just to say there could be solid reasons they don't sell to DIYers for a specific product line. As posted above, an epoxy layer would be a real pain to pull out, or an extra hassle & expense to re-coat.
Good luck.