I've got TED20 petrol/tvo version (the petrol only one is the TEA20) but if I had tha choice I'd go for the TEF20 diesel as it has a little more horsepower, but they do fetch slightly higher prices. TVO isn't available any more so you have to mix your own from petrol/heating oil - generally 1:2 ratio to give an equivalent to TVO star rating. For more details on fuel mixes look at the 'Friends of Ferguson Heritage' website '
www.fofh.co.uk' which also has a lot of other useful data.
As far as the pto is concerned it isn't live all the time - you select it using clutch/lever at the left hand side, so for trailer towing for example - you wouldn't use it. However - you do need to select it if you want to use the hydraulics/three point linkage to lift anything as the hydraulic pump is driven off the pto shaft within the main transmission.
The other consideration with the pto is that the original Ferguson pto shaft is 1 1/8" diameter six spline and while it works ok with original Ferguson equipment you will need to obtain a pto adaptor to allow use of modern equipment e.g. toppers etc which use the current standard 1 3/8" six spline shaft. Not a problem as these are readily available but if you're getting one do consider one fitted with an over-run clutch if you want to drive a topper as when you slow down the tractor the topper momentum can drive forward through the gear train putting a lot of stress on gears/clutch and brakes (and driver!).
Modern toppers etc will work perfectly well with the Fergie - I currently use a 4' topper but I know others who use 5', although they're on flatter ground than ours. Many people simply hang their toppers on the three point linkage fitting the top link to the top pin on the tractor linkage but the Fergie isn't designed to give position control for above ground implements - it only has draft control on the hydraulics to control depth in the soil, as when ploughing. This has the result that every time the topper hits a bump or change in gradient it then causes the hydraulics to adjust the height of the three point linkage so you can be forever re-adjusting the topper height to try to get an even cut. The better way to hitch up a topper is to connect the top link (tractor end) to a 'dead link' on the lower pin (you'll see that when you look at one) which does not feed back into the hydraulics so giving better control. To my knowledge 'dead links' are not commercially available so you'd need to fabricate one.
One site I've found invaluable in dealing with repairs and maintenance issues is The Grey Fergie Forum - '
www.greyfergieforum.com' - huge amount of information there including a library of handbooks/manuals freely downloadable, and the members are a very knowledgeable bunch who've helped me enoormously in dealing with my various repair jobs. Generally spares are obtainable but be wary of Eastern copy imports - they don't necessarily fit nor are they an exact copy of the originals; Sparex parts are a better bet.
Hope that's of some help and good luck with your search for one.