My MIL spent her career teaching kindergarten, and she said it take at most two weeks for the children who didn't go to preschool to learn the ropes and be indistinguishable from the children who did.
I would look for a free moms group that meets at the park. At this age it's mostly for mom, but it's invaluable in a society where new moms are no longer surrounded by extended family to provide support and advice. Sometimes community centers also run these kinds of groups. Don't worry too much about weather, as once your wife chooses a group she likes she'll find they make alternative plans if the weather isn't favorable. Libraries sometimes have tiny tot story hours. I used to take my children to story hours at the local children's bookstore and independently owned toy store, as well. If you attend a house of worship you may find programs for mothers and babies there as well, or your wife may start one.
You could use Meetup or other group websites, or just hang out at the park and see when parents of little ones are there.
I would totally save your money and skip the groups like Gymboree, Kindermusik, etc. They prey on the insecurity of the parents and warn about socialization, etc. without anything to back it up. Put the money in a college savings account and pat yourself on the back for being smart.
We homeschooled, so I heard the socialization questions and judgments nonstop for 19 years. People think socialization only happens in same age groups, and in paid classes, at daycare and preschool, or in public or private school. But socialization is interacting with the grocery store clerk, the librarian, the post office cashier, and anyone else you encounter. It happens when you walk around the block and talk to neighbors.
Best option for the little one is a closely-spaced in age sibling, lol.
