First-Time Homebuyers Buying With $400k From Future In Laws. Need Advice on Finances, Legal Stuff, and Hidden Costs

My partner is finishing their work training (about 2 years left), and I’m finishing my degree online while working remotely. We make about $95k combined and currently live comfortably and are moving forward with buying our first home in California, even though we plan to move south in about two years.

This decision was heavily encouraged by my future in-laws. The plan is that we’ll live in the home while we’re still in California, and once we move, my partner’s parents will move in. The house will be in our names. My future FIL is providing $400k toward the down payment (most of it is already in our bank account).

We’re looking at homes in the $500–600k range and touring some this weekend. This is our first time buying, and I feel overwhelmed and unsure what to watch out for.

What are the biggest first-time buyer mistakes to avoid?

Are there specific lender or mortgage considerations with such a large down payment?

What questions should we be asking our realtor during showings?

What are common red flags that should make us walk away?

What ongoing or hidden costs should we plan for beyond the mortgage?

Any advice, lessons learned, or things you wish you’d known before buying would be hugely appreciated, ty 🙏🏽