There are plenty of visitor moorings in the first basin as you exit the lock, or go through the first lift bridge and moor at the pontoon on the left, (port side if you insist!)which is much quieter, and also means you do not need to wait for the bridge keeper to start work in the morning before you can set off, there are also a couple of slots on the other side but most are private spaces, the water, refuse point is on the right as soon as you pass under the bridge. There are also short stay mooring at the supermarket.
I did the lock single handed without problem, if you do have to wait there are plenty of chains on the left hand wall, go slow, take your time and there is nothing to worry about.
Only thing to be aware of is the wind! the dock basin is large and does not offer much protection when the wind is blowing up the Severn estuary which at times can be quite strong, in these conditions trying to moor on one of the finger pontoons can be difficult, particularly single handed and especially if like me you lack a bow thruster.
That said I have always found that as long as I make my intention clear someone has usually appeared to assist, if not, the basin is plenty big enough to make a circle and try again.