Wife starting privately funded research soon as a contract employee at my place of business where I am a W-2 employee. We file joint tax returns.

1. I think setting up a solo 401 K with Vanguard to squirrel away the majority of what she'll be getting (my own 457/403b are maxed) is best, but is there anything else one can do regarding tax optimization?

2. Would increasing my withholding on W-4 allow us to avoid the hassle of paying quarterly taxes for her? One concern I have is that since I'm maxed on social security taxes, I don't know if withholding more money will fall into the right "bucket" in the event that she owes some as well (not sure how it works if one spouse is a W-2 earning over $137,700 and the other is a 1099 earning ~$40k).

I hope I'm making sense. Forgive me if I don't fully understand the rules around this stuff, I've always been a W-2 in the past.