Can I do all my border runs for a Non-O visa through land crossings from Huahin?

If he is over 50 years old, he doesn't need to bounce in and out, he should apply for an extension of stay, based on being married to a Thai lady, he only needs to show an income of more than 400.000 baht a year or hold that amount in a Thai bank account,

Do a final bounce just as your Visa is about to expire to get nearly 15 months from it :)

Couple things wrong with the plan.

No issue at all getting a year-long, multi-entry Non-O visa based on marriage to a thai from the thai consulate in your country before you come here.

You are correct you will have to bounce out and back every 90 days, BUT the Phu Nam Ron /Htee Khee border in Kanchanaburi has been closed since covid (and shows no signs of opening up any time soon) so you're going to have to find another place to bounce out and back.

Also I believe you're confusing FREE entry stamp border bounces (which you can get 2 per calendar year) with a border bounce holding a valid visa <- which has no limit to them.

Find a border to bounce at and you'll be fine comin' in and out every 3 months on that visa and you'll be fine..