Here is a web site that might help you decide how much weight you will be towing. It is aimed at RV'ers but helps you to think about what else you might be carrying with you.
Tow Calculator Demo.
Depending on Where (hills or flat), How Often, How Far, and What Else (will you be taking anything else with you) will decide on what size vehicle and trailer you will need. Yes, a 3/4 ton truck w/diesel would be ideal but a 1/2 ton truck will do the job (depending on the above answers). I have a ck20 that I tow on a regular basis about 15 miles each way, and a few times a year a 100 miles round trip. I use a '90 full size Blazer with a 350. It has a hitch rated at 6000# that I stay under. Your numbers sound correct at 3100# for the equipment that you currently have. A trailer will weigh between approx 1200# (Aluminum) to over 2000# which will probably put the total tow weight in the 5000# range.
Can you get a "midsize" truck or suv that is rated to tow this much? Yes. Do You want to? Probably not. (unless towing on a limited basis) Why do I say this? Width of tow vehicle as compared to trailer width. It can be fun making sure the trailer axles are in your lane. At minimum (depending on what you will be doing) you be a 1/2 ton truck or full size suv. Most (possibly all) available in this size will be able to tow what you have asked about and then some. In this class of vehicles you would want to get something with a V8 and possibly the largest rear differential possible (a 4.10 would be better that a 3.43, 3.23, 3.73, etc.). Once again depending on what exactly you will be doing. If you will be doing heavy towing, carrying a lot of other heavy equipment then you would probably (preferably) step up to a 3/4 ton truck/SUV.
As for the trailer... I am using a 16', 7000# gvw car/equipment trailer which is the smallest that I would go with. I was actually looking for an 18' 7000# trailer but got a deal on the 16'. There are a lot of personal preferences when it comes to trailers but I think most will agree that brakes on both axles are a most. Some will suggest a steel deck (downside slippery when wet), mine is a wood deck (more maintenance, and not as convienent to haul dirt or gravel), dove tail vs flat (ease of loading), Tilt vs no-tilt (ease of loading), removable ramps vs tilt up ramps, under bed axles (keeps width to a minimum), and many more personal preferences. Listen to all of the pros and cons of each and decide as for what your needs are based on needs and price restriction.
Note: If you go with a 1/2 ton and some 3/4 ton truck you will need to invest in a weight distributing hitch. This will help with sway issues on any truck and is needed on all 1/2 tons for proper weight distribution.
Kurt