2017 Toyota Sienna LE - 18k miles
I had my last oil change in 8/2020 but have only put 3k miles on since then. Should I bring car in to get oil/fluids changed and tire rotation ?
I'd go a couple months more, but check your oil condition.
1 year or every 5,000 miles, whichever comes first.
@DayWalker is exactly right. Anything older than a year has got too much degradation to be able to properly lubricate the motor.
3k miles in six months or so, you're likely okay until August '21.
In the meantime, research the cost of buying some basic tools (trolley jack, axle stands, socket set) that would enable you to do both of those jobs on your front garden, what you'll pay out upfront for these will save you a lot over the lifetime of this and any vehicle you may own
