So your new to tractors, well we all were once right ?????, no time like the present to learn, try and get an experienced hand to help you.
Ditto, to the safety advice, you will want to learn everything about running a rotary mower, safety is of high priority and of utmost importance to your well being, however it should not prohibit you from learning, all of us had to do it at one time, most early on in life, others not.
That 18 acres, you need to walk and inspect the work areas for hazards, holes and dens from critters, and any kinds of obstacles.
Hills, they can be dangerous, not for the inexperienced, but you can learn, tractor needs to be ballasted, ( tires loaded with CACL or similar fluid that won't freeze ), and it would be real wise to invest in a r.o.p.s ( roll over protection system ) and a seat with a seatbelt, which you must use for that r.o.p.s. to protect you in the event of a roll over.
That 3600 is a great utility tractor, we have a diesel version of it, should not be hard to learn to operate and if it is or once you have repaired it to a field ready condition, it will last you, it is a lower center of gravity kind of tractor, a r.o.p.s can be fitted to it, and parts are available etc. if were me, I'd want that one, even though it may consume more fuel and is older, it's a good tractor and perfect for that acreage, with a 6'-8' rotary mower, depending on what you are cutting.
You will need to learn some things, never take safety for granted, ALWAYS follow good practice, and eventually after some seat time, and with some help from an experienced hand, you'll be fine, yeah I know some said different.... the object is to learn and be able to use it to do work, if you don't learn, you'll have to hire it out or it won't get done.