I've not had any white balance issues with my A1 in the Amphibico Pro housing.
I've been shooting many days in the last 6 months in Thailand around the Phi Phi Islands and islands closer to land near AoNang. Generally the weather is fine ie bright sunny skies but visibiliity has been 'variable' this season - down to 5 metres on some days. I don't go beyond 30 metres - I would need a big spade for that around here - but so far no issues with white balance behind the UR pro filter, I use the white slate that came with the housing. Although noise from gain can be more noticeable than I'd like.
As the light diminishes really have to use focus lock or the auto focus constantly goes hunting...
I don't use lights day to day - just added complications and something else to to get broken on busy day boats.
Telemacro works just fine - assuming I can hold the camera steady enough and the fish stop moving!
good luck in the decision making department
regards
Simon