The ceremony and reception will take place outdoors in the museum’s garden. Google tells us that the weather will be between 58-74F, with a 7:16PM sunset time. In other words, bring a jacket or blanket for after the sun sets!
Wedding guests are welcome to enjoy the museum free of charge before 4pm. Just go to the ticketing booth and explain you’re with the wedding. There will also be an exhibit featuring the work of J.B. Blunk called "Nature, Art & Everyday Life" running from April 21–September 9, 2018. I don't know who that artist is but you can find out.
Parking is available at the museum for $7 in the garage (look for signs to entrance on Oak Street). You can also look for metered parking spots on the street
Special note to Out of Town Guests:
The Oakland Museum is located within 2 blocks of the Lake Merrit Bart Station. Oakland is the closest airport and if you're flying into Oakland airport, you can take Lyft or Bart over, but probably just take Lyft because that's easier and probably the same price.