1. Saftey. What are you adding to become more secure?
Better belts, side protection is a big plus for safety along with offset wheels to make it a little more stable in turns.
2. Theft. What can be done to deter people from stealing it? Club, kill Switch etc....
Any of those might work. I bought a Kryptonite cable lock for mine just in case. But get theft in your insurance just in case.
3. Tires. Do they make an All-terrain type tire?
Some of the guys that are racing are running a BFG All Terrain tire on there Rhinos for racing. Might fit you well.
Thanks in advance. I am looking to build something mainly for around town, with the bi-monthly off road trip.
4. The rear seat is a must, but do you guys add springs to carry heavier loads.
With kids in the back you should be fine but it may bottom out a little offroad. If you plan on taking adults in the back than I'd be carefull.
5. Can you launch and retrieve a boat with it. HONESTLY???? (21 Nautique)
Honestly? I'd say no. But others will disagree with me on this. I think its not safe personally.