I think i would give alot of thought as to what i plan on doing with the tractor. 40 hp is sure on the light side for doing much work. And is that 40 hp on the PTO or the engine. There is usually about a 10 hp difference between the two. (example tractor engine hp = 50 hp, PTO hp = 40 hp. The PTO hp usually dictates the size of implement you can use with the tractor. The smallest round baler i know of that a 40 hp pto will handle is a vermeer rebel. That is the size and type of round baler i use. I have a 50 hp PTO on my tractor and at times while baleing thick hay that is a little green. I can tell it loads the baler up some.
I did have a tractor with a 40 hp PTO and baled square bales of hay with it. And it was asking alot to do that. In thick wind rows it would almost bog the tractor down.
Myself i have to be able to move my tractor alot with a trailor. So i need all of the PTO horse power i can get and still have a tractor small enough that it is not so heavy that it makes it dangerous to move on a trailer. I have found that when you are looking at 50 hp PTO you can move a tractor that size fairly easy with a ton truck/trailer.
I wold diffinately get a tractor with a loader on it and as far as a 4wd goes. If i thought i needed it i would get it. But at the same time if i thought i could get by without it i would. Because that is just that much more that can go wrong. And when you go to buying parts for a tractor things can get exspensive quick. Exspecially if you have to take it to a mechanic to get it worked on.
That is just my 2 cents worth.