Most two wheeled vehicles(i.e., carts)are not suitable for driving a pair, unless you drive them in tandem(one directly in front of the other, with the wheeler(horse closest to the vehicle)actually doing the work-*some*special harness components would be required. Driving tandem is rather challenging,too, and probably not for the 'brand new' driver-and might not be what you'd choose for "everyday" driving for fun-requires more room to turn your rig, etc.
What you might consider would be a lightweight, basic 4 wheeled carriage, most of which can be set up for either single or pair, by being able to interchange a set of shafts with a team pole. In general, it should be in some ways easier for a single to pull a 4 wheeled carriage, as if it is correctly set up, there should be NO weight in the tug loops, and therefore on the horse's back. Of course, a 4 wheeled vehicle is pretty much always going to be heavier; often, this would be a good reason to choose (well-fitted!)neck collars with hames(which are more expensive)over Hungarian, or breast collar, type pair harness. Pair harness has some special features-you cannot just use two single harnesses-but, you CAN order pair harness that can also be used as two singles, if you so specify. There will always be 'tradeoffs' if you wish to be able to drive either a single or a standard pair to the same vehicle(especially with minis, and their small size.) Just the reality...."I'd recommend doing lots of research before you commit to anything!
A tip: for basic training, a basic training cart is VERY helpful. If and when you get your horse(s) well-trained, you can always sell it(there's ALWAYS a market for a good used training-type cart), or keep it for 'runaround' use.
Best of luck!
