529 plan lump sum

my client just came into a 150k lump sum.

his only child is a freshman in college.

are there any pitfalls to be aware of regarding starting a 529 plan?

some random thoughts I had:

I believe each parent could contribute a max of $55,000 for a total of $110k without a gift tax

I asked the client to check the estimated costs over the next four years as it’s a five year program.

Would it be accurate to say that we’d rather underfund this account than overfund?

I’m recommending an asset mix of about 50% cash money market, 25% fixed income and 25% blue chips for growth.

I just never had a case before where they were contributing to a 529 while the child was actually in college already.

Thanks in advance for any valuable feedback.