So... I'm actually having a hard time finding a mod (or mods) for this but basically, I'm looking for a mod which improves on relationship building and more actions you can do later on with your spouse (rather than doing a quest, getting married, and then do almost nothing with them from then onward). Please note, I'm talking about with any marriageable character, I'm not looking for "custom marriageable characters".

So anyone have any ideas/recommendations?

I don't know of any, but would gladly like to find one or more myself. There may not be such a thing, Closest I have found is http://www.nexusmods.com/skyrim/mods/11450/?, Add lots of content to do with Aela after the Companions questline. Unfortunately the problem with her losing all personality if you want to get married remains. I am hopeful the author continues to build on his mods, I like them both a lot.

There are not many. Theres one with the vendor in whiterun where u marry her and adopt her daughter
I know you set the criteria but interesting npcs has one where you go on dates and there is romance