Well - Here's my 2 Cents worth.
I have had a few MV trucks.
Now remember - this is from my point of view and everybody is different, so ..........
I enjoy playing. Don't get me wrong, I have done engine swaps and stuff. But to be honest with you, that was more than a couple of years ago and I'm not getting any younger. I tend to do a lot of my projects on my own which means that big projects are big work. I have found that I enjoy playing with the trucks (along with the necessary tinkering and maintenance included) much more than the heavy wrenching. I have many friends that just love a complete tear down, etc., but I can only speak from my experience.
The point is - figure out what you want to do with the truck(s). Remember, there is only so much time in the day. If you are one who is a born mechanic and loves being under the truck more than in it (again, I know many who do - never get a hot rod past primer because all of the "creativity" is done so the rest is just work) then by all means buy a project truck and have fun. Just remember - big toy means big parts and big tools. Many of these tasks can be dangerous if not done with the proper tools and experience. Sometimes I wish that I had those types of skills and determination. My hat goes off to the restorers (a certain Damon and a HEMTT come to mind!) On the other hand, if you are as I am and end up spending more time playing than wrenching, I have found two things that were a plus. First, get a vehicle that is the "easyest" to operate. This is not intended to test the wimp factor. By no means, as far as I know, the heavier the truck - the more probable it is that it has power steering. Definitely a plus in my book. I have had 3 different styles of deuces (M211, M34, and M46A2C). Trust me, until I got my first 5-ton (with power steering), I didn't know what I was missing. All of a sudden I could enjoy more and grunt less. And remember, the deuces and 5-tons are both 8' wide, only a few feet different in length (with standard wheelbase) and deffinitely worth the difference in weight. There are other things to consider such as transmission. One 5-ton that I had came with an Allison Automatic. Very cool and very fun. Second thing if your just out to have fun - get the most complete, best running truck you can. The last truck I bought I did so already restored. Got in, fired it up, and just had fun. And you know that I still admire the guys who did the restoration. Even though I paid for it, I can't help but marvel at the work that goes into much of these trucks (again, big truck = big project).
Next - figure out how much you have or want to spend on a new toy. This is almost as important as what you want to do. I have found that, if I can afford it, sometimes I just can't deny that I get a better product by buying it from those who know exactly what they are doing (and have done it many times before). If finances are an issue, then this may answer a lot of the other questions. If you can spend a little more sometimes you can wrench a little less.
Well, I guess I have babbled enough. Hope you can get something out of this.
Good Luck
Dave