"It is important too, not to fund too heavily the cards"

Could you specify this? Also, if you don't fund them heavily you have to use them around the year to reach the limit which should make it looking less legit considering it's a debit card being used for holiday or something.

"They will reply to you and require to send back your passport scan and a justification of funding sources."

Only passport works or other picture IDs too?
What kind of proof is needed?