Only way to accomplish this currently is by way of CBSubs, which do not have to have a price. This is done by hiding fields at registration with a CBSubs plan (Workflows tab).

1) I want two different groups, lets say actors and directors. Actors will HAVE TO upload at least two photos, while directors can only upload one (as an avatar). While the same thing happens with other fields that are mandatory for directors while actors should not see them at all. I also want the profile page to be shown in a different way for actors and for directors. Is this possible?

CBSubs plans can hide fields based on plan select so for instance you can have a required field that we'll call Field A and two plans called Plan 1 and Plan 2. You can hide for the field on registration for Plan 2 and when a user clicks Plan 2 then Field A will not be displayed or validated against.

2) I want to create a search engine where the registered usere can search for a specific field, lets say an actor above the age of 30 or a director living in Athens. Is this gonna be a problem working with CBSubs?

You don't need CBSubs for this; simply create a CB userlist in Userlist Management which allows searching of users based on fields.

3) Can I really make this look nice without the user noticing it's a workaround? i mean i want it to look like a registration and not like a subscription.

You're able to remove the price so all users would see is 2 radio buttons to select the 2 different profile types. You can also style it further using CSS.

4) If I buy CBSubs can I use it for other sites also? or i have to buy another copy / licence?

1 License = 1 Live Site & 1 Development Site

You are also limited to the amount of users based off the license purchase.

I also might suggest that I am working on a "Conditional Fields" plugin that will allow show/hide of fields based off another fields value. This project would be released to the Incubator (accessible by Professional subscribers). This could be an alternative for you, but I don't have a time frame for release aside from 1, maybe 2-3 weeks from now.