Welcome! Glad you found your way to the forum. Lots of experienced reef keepers on here who I am sure will be happy to chime in with suggestions. Personally, I have had a couple of 125 gallon tanks and do think that is a good size to work with. Large enough to be relatively stable but not so big it’s hard to maintain. Also can accommodate a wide range of fish except for mature specimens of tangs, triggers etc. so fairly flexible for stocking. Just remember that other elements (lights, skimmer, pumps, reactors) will need to be scaled appropriately so know what you are getting into before committing to a large tank. I do think, however, that there are some economies of scale involved.
As for automation, you should check out Suncrestreef’s build and Apex controller threads - lots of great info on how to set up automated testing, dosing, water changes etc. - he is the Apex whisperer on the forum.
If you search with keywords you are likely to find lots of threads speaking to the husbands questions - especially around coral and fish diseases, pests and hitchhikers. These always make for a worthwhile read.