Rod, I am in Australia and this might not be relevant but it sounds like you are in the same boat as a lot of small acreage owners in oz. I would say that you need two saws. The first would be a lightweight 40-45cc saw. There are many of these around, but I would really keep an eye out for something like a Dolmar/Makita PS-400, or similar.. These are old, but a really good lightweight saw that will handle all small work with ease and cost not very much. Run a 14-16 inch bar on it.
Then you need a bigish saw. Big equals about 70cc. If you can get a lightly used pro saw second hand you should. Husky 268/72 or 365 are great landowner options. I love Dolmar/Makita and would look for any of their bigger saws at a significant price reduction over Stihl/Husky. The money you save on getting a big saw like the Dolmar allows you to pick up a small saw as well for the cost of the Stihl/Husky.
You want the small saw to be as light as possible in the 40-45cc range. It is the one you will end up using the most.
Whatever you get, make sure you run three chains on each saw, swapping the chain after each major usage after you have sharpened it. If you have an air compressor great, blow over the saw after each usage. If not, at least brush it down and store them on a shelf off the ground. Larn how to sharpen the chains and adjust the tension. Always use good quality 2 stroke oil mixed at 40/50 - 1 and use high quality bar oil.
If you are a little bit handy, consider getting something a little older as the big saw (you wont use it that much and it can be a bit of a Hobby). The internet is full of information re keeping an older saw going. I personally have a Dolmar 120si and a Mcculloch Pro Mac 850 which are cracking big saws that would handle any farm situation - lots will say go modern, but if you have an inquiring mind there are many great options out there. I reckon I see 10 great saw a week for sale in Australia - you have access to 10 times that many.
For what it seems you need to do I would really urge you to learn about saws and make them something that you master a knowledge of. If you do this whatever saw you get has the potential to last you a very long time. The best saw treated badly wont last very long - but any saw treated well is a wonderful working tool. Good luck.