To set the chain tension, remove shocks, pack wheel up until the centre of both sprockets and the swing arm pivot are all in one line as close as possible then tension chain to give just a small amount of slack (about 10mm) and tighten wheel.
Then put shocks back on, and measure the slack in the chain to give you an in use set point for future adjustment.
If you set it too tight with the swinging arm extended downwards then as you ride it, when the suspension compresses it will go to tight at its longest point and pull the hell out of the bearings, particularly the gearbox output one.
Build looks good by the way.
Tires look good, I've used them on lighter bikes (kdx250) on the road and they are pretty good but squirm quite alot with front brake use so may take a bit of care to get the feel of them if you've not ridden with them before especially with the weight you'll be carrying on this bike.
