All sites say the same thing

[Sepone]

Ok I’ll marry on my next playthrough. What are some main benefits for marrying? Does that essentially mean I’m allied with my wife’s faction? Getting their armies under my clan too?

No, you're not automatically allied or become a vassal, it is the other way around, she'll join your clan. You don't get any armies! Your wife is a free companion (doesn't count to companion limit) with very good equipment, some are good fighters and army leaders, too. They are also good for governing fiefs, but their main "job" is creating heirs.

 

[Ananda_The_Destroyer]

Benefit of marriage is currently get about +30 relation with spouses clan, get spouse as additional companion, get to take spouses equipment which may be high tier armor and not available in stores in your game. In the beta the husband only gave me 30 10 10 body armor, but in the older builds he had 48 20 20 armor. Not sure if it's just random or if other lords could still have the good stuff.
I want the good stuff!

 

[Ncallstar08]

Do I get to have her do quests, lead parties, caravans? Stuff a normal companion would do? And my plan was to marry on my second playthrough since I can’t marry now I’m too old.

 

[Badcritter]

One wonders why you can't marry past the age of 35. I can't think why that should be restricted from either a gameplay perspective or a lore/realism perspective. Even the issue of fertility for a female character shouldn't preclude marriage for political reasons.

 

[Sepone]

Do I get to have her do quests, lead parties, caravans? Stuff a normal companion would do? And my plan was to marry on my second playthrough since I can’t marry now I’m too old.

Yes, your wife will be like all other companions!

One wonders why you can't marry past the age of 35. I can't think why that should be restricted from either a gameplay perspective or a lore/realism perspective. Even the issue of fertility for a female character shouldn't preclude marriage for political reasons.

Yeah, doesn't make much sense.