Answering your last question first - the recommended hydraulic oil for your Serial Number is an SAE10W viscosity hydraulic oil with a zinc-based additive package. Pretty well every lubricant company on earth will produce one.
If you don't have one already then you should get hold of an Lubrication & Maintenance Manual. The Cat Publication reference is GEG00535. You can get a copy in CD format from the Cat publications web site for $30.
Now to your first two questions, which is a much more complex subject that needs a lot more information in order to answer. First up, approximately how many hours per month/year are you looking at operating the tractor.?
Next is that the undercarriage is a system consists of far more than just the tracks. The condition of the following influences the system operation.
Drive sprocket
Track frames, track guiding guards/hardware (if fitted), and pivots
Equalizer bar and suspension
Track rollers
Carrier Rollers
Track tensioner & Recoil mechanism
Front idler and mounting.
So I guess your first task is take a shed-load more photos illustrating the condition of all the above.