the tank is vented because the pump draws a vacuum. with no vent this would cause a vacuum in the tank and not allow fuel flow.
I usually route my vent line through the bottom of the fuse and put a check valve in the vent line so that air can enter
but fuel will not spill out. You may find it easier to use a 3 line setup on this plane as it has a cowl. I use a fill line with a fuel dot
to fill the tank and remove the check valve from the vent as my overflow when filling. and the fuel line to the carb stays connected during fillup.

Install the engine and pump, and start the engine for breakin like you normally would. as long as the engine runs rich enough to 4stroke
you are OK. I have 2 OS 1.60's with Vp30 pumps and neither of them needed any adjustments during breakin, the adjustment may be needed
after breakin to lean the engine out.

The easiest way I know to prime is, open throttle to full, flip prop 2-4 times by or until you see fuel at the carb. (you don't need to plug exhaust or finger over carb
the pump starts working when the engine is turned). put igniter on and hit the engine with electric starter.

Yes the fuel line from engine to pump is supposed to be rigid, the pump works on pressure pulses created in the crankcase, a flexible line will absorb the pulses and
the pump will not operate properly.

Don't forget to plug off the pressure tap on the muffler it can make an oily mess.