Snakebit - it's not absolutely necessary to remove every last drop of the old
oil. Assuming you are changing
oil frequently anyway, so you are not exactly leaving sludge in the
oil lines. There is life left in the old oil.
On the pressure question, you can pour some of your new oil into the new filter, so basically all that needs to fill up will be the lines when you first crank the engine. This will help the pressure come up quicker.
My car has an Accusump, and I switch it on before every cold cranking to pre-prime the oil system. It will take the pressure up to about 35 lbs before starting.
Lynn