I've owned two chippers in the 36 years out here. Wallenstein BX42S and now Wallenstein BX62S. I can only speak on Wally's - maintenance has been almost zero. You have two zerks to grease and I grease the four cutting blades before putting it up for the winter. Oh, and grease the PTO shaft once a year also.
Both my Wallys were/are manual feed. Every year I thin my pine stands and chip approximately 900 or more small pines( 1" to 6" on the butt). There is nothing quite as easy to chip as a fresh cut pine - soft wood - full of juicy sap - no limbs to trim - just cut - drag - pile - grunt/lift into the
chipper.
I would imagine your oak limbs will be twisted and gnarly. You would be best served to get a
chipper with hydraulic in-feed. Controls the feed speed and can back out those limbs that will tend to get stuck in the chute.
But again and at least for my manual feed chippers - - maintenance is just one tick above what is required for a hand shovel.
My thinning project is every spring - takes about six weeks - worse part is dragging all the cut pine out and piling them. The chipping part is the fun part.
For me the choice of buy or rent was never a problem. In the middle of millions of acres of cattle ranching - I am 80 acres of tree farming. My choice was - which brand. Beyond Wallenstein I looked at Woodmax and Vermeer. I wanted a PTO driven
chipper - the local Kubota dealer gave me good prices on Wallenstein - - this choice was simple also.