Sorry, Man this question is a bit like how long is a piece of string! You'll have to experiment!
Can I suggest possibly sticking the velcro to the stand you intend to use then using pieces of velcro on say a piece of scrap wood (possibly the same or similar weight / dimensions?) and seeing how much works for you? I know you'll possibly be wasting the velcro you stick on the wood but it maybe worth the cost in the long run?
How about using a picture frame stand for the time being instead see if that works for you?