To take the plaster off before it comes off, don't pull it upwards because this hurts like the blazes. You can use hot water if you like, but tease the edge up and pull it ALONG the skin slowly as flat as you can.
They get a white spot above the blister or sore - this is where the gel is acting as a drawing poultice to draw out the fluid or pus away from the wound. This is a normal thing which happens with the gel bandage and it is supposed to help the healing. It also keeps a microenvironment stable around the wound so it doesn't get damp when you have a shower (unlike band aid type things which always leak).
And yes you are supposed to wash and dry the wound first. Also don't put stuff on udner the bandage; no savlon or rawleighs.