The grease injectors fill the cavity with grease and any excess is pushed out the front of the freewheel. It's like greasing an old car suspension where you pumped in grease until it squeezed out of the joint.
Yes, the pawls are spring loaded. That's why they "click". The pawl is springing back into the teeth on the freewheel. But sometimes the pawls get stuck because of contamination. Fresh oil will usually free them up. If it doesn't, just get a new freewheel. They are cheap.
Two issues here. First let's talk about the hub. At some point you are going to bend the axle in the hub. You may even break one. That's not a maybe, it is
going to happen. Freewheel hubs have too much axle sticking out from the bearings with too much load on them. They will bend and the more weight they have to carry, the sooner they will bend. In fact, you might check that now because that could interfere with the spinning of the hub and the freewheeling of the freewheel. Spin the axle with the wheel off the bike and see if the axle is moving up and down on the drive side.
It would be better to convert to a freehub hub in the future when this axle fails. The freehub design puts bearings out on the ends of the axle which makes them much less prone to bending. I've yet to see a bent freehub axle. That doesn't mean it
can't bend but it's just a lot less likely.
Second, the rim has very little to do with wheel strength. Rims are a convenient place to put spokes and make using a tire easier but from the standpoint of strength, the spokes do
all...as in completely, as in the whole enchilada, as in totally...hard work of keeping the wheel strong. This picture illustrates how the spoke react to weight, cornering, acceleration and braking.
wheel by
Stuart Black, on Flickr
It shows (in an exaggerated form) how the
spokes are reacting to the forces placed on it. The rim is just along for the ride. Make the spokes strong and the wheel will be strong. I'm not your weight but close. I also load my bikes up with a bunch of stuff for camping and ride both on- and off-road while doing so. I use DT Swiss Alpine III spokes which have a thicker head which increases their strength by about 50%. I use super light rims and strong spokes without spoke issues I used to experience when I use lighter gauge spokes. The upshot of this is that you don't need heavy rims to have a strong wheel.
DT Swiss Alpine spokes aren't cheap but they are worth the extra cost if you aren't replacing spokes and/or wheels all the time.