How stiff should the trucks be?

You can easily adjust them, so don't worry too much. They don't have to be very loose, because you automatically lean hard when locking into either edge. When you start learning how to carve, you might wanna make the front truck looser than the back, but that's optional.

If you make them too loose, you'll probably fall off. Don't worry about them being too stiff, you'll understand how easy it is to carve when you actually start riding. Also, the bushings will ease up after some use.

Your bushings will loosen up after a while of being on it, there is a break in period. Not sure how heavy you are but I got the green, hard bushings from the FB web store and they are better in my opinion (I'm about 175-185, 6 feet). Typically stiffer trucks are going to make it more snowboard like, carving will be wider, and slides will take more waist action to initiate. Looser trucks will increase your carve and will be more carving-board like. Looser trucks will also make initiating slides more of an ankle/weight placement deal and can cause 'auto-sliding' and 180 spins without you intending to if you get them too loose and you are not practiced with it. It's true if you want even deeper carves to loosen your downhill side trucks more so than your uphill trucks, but this will make riding switch really had to learn. I also lower my downhill caster 1 notch lower than the uphill caster, which is on it's maxed\factory setting. (I don't usually ride switch) I feel like this helps me initiate slides better and carve deeper with stiffer truck settings. Also, hill steepness and speed will play a role in how tight you want your trucks. Faster you're going to want tighter trucks, unless you plan on slooshing down it then you might want somewhat looser. Neighborhood freeride you are probably going to want to go on the looser side. And it all depends on your weight, height, and how tall you ride, and really just what you prefer the most. This is the most common and hardest question to answer. I think in the end I like specific settings for specific hills and ride styles, sometimes I like to go really fast and sometimes I like to carve and shred it up.

Also as a point of reference I would say that 'loose' to me on a Freebord is still pretty tight when I compare it to my carving board. It's basically a normal street deck with Bear 852 trucks, angled riser pads and factory bushings that I tightened up. They still feel much looser than the Freebord. I would say the carving board definitely can carve tighter, but the Freeboard can slide on a dime and make the same turns.