I'll try to respond to your post on a point-by-point basis.

I can't speak about the global market, but in the parts of the photography industry that I've brushed with, the only people who care about your CV are fine art buyers, museums and schools. In all other areas, they only hire based on portfolio.

A good rule of thumb for me is "Let them be concerned with their concerns, and let me be concerned with mine." They want you to fill in? What do you want? Are you working elsewhere? When does your schedule fill up? This is the best way to determine how much advanced notice you need for scheduling. Once scheduled, an assignment should be in stone for you, subject to cancellation only by the person paying the money (ie, don't try to cancel scheduled events for better paying gigs-- it's rude).

Use of the studio by those working in it is what might be called a "standard perk." Yes, it is very nice of them, and certainly a show of trust if they let you use it without supervision, but it is also a pretty common thing.

By law, assistants in the US get paid a flat daily rate for a 10 hour day, which includes 30 minutes lunch, and two 15-minute breaks. For every hour beyond the 10, we charge an overtime rate equal to (DayRate / 10 * 1.5), time-and-a-half of the hourly-equivalent rate. I charge a half-day rate, 5 hours for roughly 2/3rd of my Day Rate. Again, this is based on US Law. Find assistant photographers or other types of freelancers and sub-contractors in your country and ask them about it. The assistant photographers should be able to give you an idea of a standard day rate.

In the US, the specific services I perform for the day are irrelevant. I get paid on a per-day basis. I might have a relationship with a photographer or studio where I can bring my own clients in on off-hours and rent space and equipment from them, in which case I am the active studio, and regardless of my relationship at other times, they are my assistants and rental company. The deciding question is, "Who brought the client?"

Copyright law is a really complex question, particularly as you cross borders. I wouldn't want to be held legally responsible for any opinions you hold. Normally, I would direct these questions to the ASMP( www.asmp.org )or the APA ( www.apanational.org ), but both of those are American organizations. If you'd like, I can ask them for the equivalent organization in your country of origin.

However, the base of your question is whether you are their employee, or a sub-contractor they regularly work with. In the US, this is a very important distinction, as employees are entitled to a range of benefits which sub-contractors are not.

I hope this helps.

They had chained him down to things that are, and had then explained the workings of those things till mystery had gone out of the world....And when he had failed to find [wonder and mystery] in things whose laws are known and measurable, they told him he lacked imagination, and was immature because he preferred dream-illusions to the illusions of our physical creation.
      -- HP Lovecraft, The Silver Key