I would kill for 65 acres of pasture lol. My jaw dropped when you said 65 acres of leased pasture, I would assume that's a $500 deposit?
I have been trying to rent pasture for some time, anyone around here with the fence for cattle usually say piss off to $30-$60 an acre because they can hay it or have horse people rent it for lots more money, pasture renting is basically just keeping the grass cut down by livestock, that's all.
If I was you, I would kick the farmer off, kill all the grass/weeds, disk it and drill new quality pasture grass seed, around here a timothy/ orchard grass/ alfalfa mix/ clover mix does best.
After it's planted in new grass I would either have a local farmer hay it or I would stick 40-50 head of cattle on it.
Cattle are easy to take care of, just give them 1-2 acres per head and fresh water and let them fatten, Finnish them on corn or whatever you prefer.
Having a hay field keeps you from having to cut it, the farmer usually cuts it 3 times per year for hay, depending on your grow season, you and the farmer can work out the split.
The property the farmer rents is generally his responsibility, he mends your fence, he manages the cattle and replants bald spots ext. he should cut the grass if it seeds, grass that seeds stops growing and dies, it should be bush hogged if it goes to seed because the cattle can't keep up.
He should manage the ground for proper pasture rotation, pasture needs to recover from cattle, in order to keep the grass growing good a pasture rotation is needed.
He should fix any and all damage done by the cattle, every few years the pasture should be rejuvenated with a pasture rejuvenator, cattle pack the crap out of the ground which stunts the grass growth.
He may wish to fertilize the grass during a rotation and spot spray weeds with 2,4-D or a stronger herbicide. He should treat his cattle with a insecticide to keep the flys down, I treat and have fly traps around the property.
You won't smell dung unless the cattle are overcrowded like in a barn, if he sticks to 1-2 acres per head it won't be a issue.
As far as clearing pasture goes, buy a 40hp+ tractor, bush hog everything under 4in, chainsaw the rest and bush hog the over growth, that's where I would spray it with round up of a strong herbicide to kill everything, disk/drill new seed.
For that you would need a bush hog, 6-10ft disk or tiller, rent or buy a drill to plant.