Hello Ketkew,
Let me answer your questions one-by-one:
1. If you want the Upload Photo service to be available for free - you can disable this action in the User Credits plugin settings and it will not be counted by the system. Also, if the action (for ex: Add Photo) is available to a role, this action won't also be counted by the User Credits plugin.
2. Yes, it's possible. You can set a positive value for any action (including Daily login, User join, Birthday), so then a user will be given by the amount of credits you set in the User Credits settings.
3. Could you please specify what you mean by saying 'receive 100 credits by default after defined'. Do you want all your user to receive 100 credits after you will install the User Credits plugin? No, it's impossible. There are the list of available actions a user can receive/spend credits for. So, all you can do is to set the 100 value for, let's say, Daily login action and if a user logs into the site, they receives 100 credits.
4. Yes, all our plugins work with the latest Oxwall software version.
I hope my explanation is clear enough. If not, please don't hesitate to get back to me for clarifications or additional instructions.