2 Jan 11, 2020 10:34
Re the last part : It is not a problem for the database as it only stores the info.
Re multiple groups : Any user can be a member of any group. You will have to make them a member of each group via Group Permissions. Go to group permissions for each collection you want the member to be a part of and give them permissions.
What you may want is under Site >Users is to have boxes for each collection in the row for each user so than you can just check a box rather than go to each collection manually. It does make sense in that it would be easier, but you can do it as mentioned, if you didn't already know :)