Determine the highest performance you want to fly and go for whatever you need to support it. The lesser performance can well operate with less.
Some things that you might consider:
Jets and large competition scale models will generally need brakes. Braking is not feasible on grass as a skip across a grass clump, brakes lock and so goes the gear. If you can make a grass RR of some 700' +, then brakes will probably not be needed. Grass is easier to operate off of as the ground steering is not nearly so critical.
Overfly of property not yours can well create havoc for recovery of a down-plane. AMA recommended distances require some 50 acres +/- not including parking. Big Birds can easily use more. How much area and who are the neighbors?
Will you be pylon racing? AMA specifications are woefully inadequate for 3-pylon race courses unless the entire area is just one big runway.
Do you fly combat? AMA field specs. also inadequate for RC Combat under current Safety Code and rules.

I suggest as large a Pit area as you can afford.

Now for runway orientation: Do as we did, Study the average wind direction etc for past 10 years. Lay out runway for best chance of headwind, north-south, east-west take-offs & landings which for us was a 16/34 runway. Now for the past 8 years we are assured that each important flying day such as a sanctioned event etc., that we have a near 90* cross wind. Go Figger!

Best of luck. Enjoy!