Understand that a forklift's rated capacity is based on a 24" load center, the center of a 48" pallet with the forks fully inserted in the pallet. That may be an important consideration if you plan on lifting loads with a load center farther out than 24". Adding counterweight to a forklift that is not designed to accept more counterweight is in violation of OSHA 1910(q)(6), and is unsafe. Having said that, you can lift a load farther out than 24", but the capacity is reduced. Let's say the data plate states a capacity of 4,000 lbs. @ 24" load center, 4,000 x 24 = 96,000. 96,000 divided by 36 = 2,666 lbs., so your 4,000 lb capacity forklift is now reduced to 2,666 lbs @ 36" load center. The most common forklift type is the class 5 counterbalanced pneumatic (air) tire type. They can be used indoors and outdoors on concrete, asphalt and packed gravel, but not rough terrain, it may get stuck in dirt. A solid tire (class 4) also called a cushion tire lift, can be used outdoors on level concrete and maybe asphalt, but they can sink in if the asphalt is hot. Solid tire forklifts also have a lower ground clearance and don't do well on ramps or uneven surfaces, they can high center and be very difficult to move once stuck. Electric forklifts are fine, most are solid (cushion) tire, but don't do well outdoors. The battery can be very expensive to replace, in the $1,000s of dollars, and you need a 240VAC charger or you will be waiting 24 to 48 hours to charge at 120VAC. I'd stick with an LPG type, pneumatic tire, 4,000 - 5,000 lb capacity. I've been involved with forklifts for over 40 years, have trained over 5,000 operators, and 1100 instructors. I'm now semi retired and only do forklift expert witness work.