You can't bring Ysolda with you on adventures like you can with Lydia (and Mjoll for that matter).
You find Ysolda in Whiterun, near the marketplace. She wanders up and down in a skyblue robe.
I made 4 different characters and 2 of them I married. First one with Aela the Huntress (from the Companions Guild in Whiterun). The second time I married a mage girl from the Mage College.
Both Aela and the mage were nice to have around. Aela uses bow alot and has sneak, so thats handy if you are a sneaky character yourself. Lydia (and Mjoll, Uthgerdt and other heavy armor companions) all make alot of noise, so tougher to sneak up on mobs.
As for the shop question, the mage one I married and had with me on adventures also opened up a shop when I told we had to seperate for awhile. I parked her at home on a quest where I knew I'd have more use for Lydia and her tanking. When I got back home the mage wife said she had wanted to open a shop, and so she did. So I got money (100g per day) from her anyways.
So you don't need Ysolda to have a shop in your home.
So far I found Lydia to be the most useful one (and yes you can marry Lydia, but there is a trick to it... you have to open the Console, click on Lydia, then type in Addtofaction 19809 1 ... then you can ask Lydia to marry you if you wear the Amulet of Mara).
What I didn't like about the mage wife was that she was just wearing rags and I couldn't get her to look nicer by giving her some nice looking robes. She just wouldn't wear them. So I prefer the heavily armored girls like Uthgerdt, Lydia and Mjoll, or one of the other armored girls such as Aela, Njada and Ria (all 3 from the Companions guild). At least you can put some nice armor on them and have them look good too

I never bothered with marrying the girls that you can't bring with you on adventures, so if there is any benefit from the non-combat wives like Ysolda and Camilla Valerius, please post it. And like I said, the other wives also open up a shop and give you money, so thats not a benefit exclusive to non-combat wives.