Albergue Casa Baztan has availability on berking.con from 1 July. Albergue Camino del Perdon is said to be opening from 1 July. Given the fluidity of current events I would wait until much nearer my travel time before making any commitments.
Uterga is not a great distance from Zariquiegui. Depends of course where you begin! The idea of getting a taxi back to Pamplona is ok, but with sufficient mental energy, and a booking at the albergue on the left in Uterga, with its range of options from bunks in a common dormitory to private rooms, and an option for dinner, strikes me as achievable. I did it very recently, but before Covid, from Pamplona, and it was a delightful day.
It is good that you walk at your pace and distance everyday. What is easy for some can be difficult for others. Pick the distance you think is right for you. You can adjust daily as you watch the weather, and experience your own bodies. Walk your camino not someone else’s.We are older and the idea of walking 10 miles a day for 50 days is a little scary.
Our first Camino in 2008 hurt a bit as we rushed because of the terrible weather when we commenced in May. The albergue in PLReina was closed under water.I walked to Zariquiegui from Trinidad de Arre, then got a taxi back into Pamplona, did some sightseeing etc, took part in the fiesta that was going on with old friends and next morning got a taxi back to Zariquiegui.