1) easiest way is to remove the swivel from the axle with the 6 bolts as described, easy to pass the seal over and affix onto the housing. Drain all the oil off. You can actually do this with everything still attached and the halfshaft will come with it, but that probably isn't the best idea as it'll be rather heavy indeed. I'd remove the stub axle and half shaft first but it is up to you.
2) I'd use EP90 as originally recommended. One shot grease is usually used when people have poor chrome or seals and the oil leaks out everywhere. Good seals and chrome and you won't have a problem with the EP90, plus the splash lubrication is much better with oil.
3) Possibly, but given the price of the new bolts I'd be inclined to replace them all anyway. Will certainly make it easier in the future. The nuts are nyloks I seem to recall, so should be replaced with new ones anyway.