There's no fundamental differences for foreigners getting mortgages. I would suggest already going to see an advisor at your bank (and maybe a few others to get other offers), to discuss in general terms how things would work for you. You really don't want to wait until you're making offers to at least have had preliminary discussions.
With respect to loans from your parents, that really is up to you and how you get on with your parents. There's certainly no obligation to have a notarized document or indeed any document at all, but if you feel more comfortable with that you can obviously do so.