My best guess would be 1983-1985 range. They made the B7200 from 1983-1990 and based off of the S.N. it appears that it was in the early production years.
Although I am not familiar with this particular tractor, I have done some research and found that it is very highly rated. I would suggest looking for some reviews of this product and decide if it has the options you are looking for. http://www.tractorbynet.com/guide/Kubota/b7200/reviews http://www.compacttractorreview.com/review/Kubota/B7200.aspx
I believe that the kubota b7200 is good for farming because it's a really big and can be used for digging really big holes and if you're that type of gardener then you're set.
http://barrelpoint.com/cgi-bin/tractor/fullThread.pl?catcode=KU&catname=Kubota%20Review&parentnum=10824&page=1 This website has reviews about the Kubota B7200. There are many pros and cons about it. It averages $4000.
This is detailed in the Maintenence and Do-it-yourself section of your owners manual. Owners manuals can also be viewed online from Nissan. The cabin air filter is behind the glove box. The glove box must be opened while pressing both sides in until it hangs down completely. Remove the filter cover bolt and then the filters. Replace the filters(two come with each set). Replace cover and glove box. Go to this site to purchase the filters and/or to read about how to replace them. http://www.xterraparts.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=Xterra&Product_Code=B7200-00001