Those are great questions. I'll try to hit them in order.
About the pure legal aspect, as with any country, there's law theory and law practice. Here's theory: It is against the law as a man to pay for the services of a prostitute. It is a felony to use a prostitute who is under 18, who is not in her right mind, or is in dire straits and must resort to prostitution to survive. It is also highly illegal to promote prostitution by hosting a website for that purpose or setting appointments etc. I would have to look in my penal code to cite you the different penal code articles that refer to this, but I encourage you to do some research yourself by getting a PDF copy of the penal code and browsing it.
Here's the practice: Most of the time, as two adults consenting to prostitution, you'll be okay. Now that doesn't mean you're immune, because they can charge you with these crimes in addition to other things if they want to.
Let's keep in mind that the word "donations" does not change the nature of prostitution in Baja California at all. It's semantics. The penal code defines any type of exchange, even gratuity, as to violating this code. So when they say "donations", they might as well say "hourly rate" because in court it would be the same thing. "I didn't punch him, he ran into my fist." That kind of thing. It's silly.
Now, when you're in a hotel room for instance, you're technically legally considered in your domicile. This is your home and no one has the right to enter, not even hotel staff without either your permission, or a suspicion of danger or destruction of hotel property. The police cannot enter without a warrant. This does not mean the police will not just break down your door anyways, but it's unlikely. Again, theory and practice.
Keep in mind that stings in Mexico - operaciones encubiertas - are not legal. Police can infiltrate criminal organizations for intel, but they cannot directly do sting arrests or use any of that evidence in a court of law. There's a zero chance that a client or hooker is really a cop. Even if she or he was, it would be thrown out of court and the officer charged under article 192 of the penal code, which is abuse of authority.
Here's my stance on negotiation. I do not negotiate because I feel like if a woman feels like she is dropping her rate, she will drop her service quality. You set the price. I buy or I don't. Set it reasonably, and more people will buy. Set it too high and they won't. I am the selector, not the selectee. They are trying to attract business. I don't go the grocery store and negotiate the price of food. If it's too much, I find another store.
I'm not into cuddling and kissing. With making an appointment I have a purpose of relieving anxiety without having to go through all the other hoops of answering to them or trying to entertain them or cater to them. If they want a man to carry on a conversation, to cuddle and kiss, well, I'm here, but I'm not paying someone for me to indulge them. The minute it costs money, it's for my enjoyment and not for theirs. However, everyone has different tastes, so if you feel the need to pay them and to kiss them and cuddle them, then by all means, proceed.
As far as communication, I don't really ask up front. I like the encounter to feel like a casual encounter. If I pay them and they don't do anything that I like, well, then they don't get a second phone call. So far, I've hardly ever been disappointed. But then again, I just need them to assume the position and let me release some stress I've built up all week. I'm not trying to be having sex for 4 hours and doing a circus act in the bed. Plenty of other men out there do those "all nighters" and like to get fancy. If you have a specific request that is not the norm, like anal things, then you should probably ask if they do it. Stay away from all the slang - it's tacky. Just ask and keep it simple.
The working out of the time and all is up front. Most of the time for agencies or collaborative websites, it will specify the services offered or you can ask on the phone. When I call up, I just say "I was wondering if you'd be free for an hour around 8pm?" They'll say "8? 1 hour? Sure. Where at?" Then there you go. It's pretty simple.
All that talking in code that it sounds like you have to do unfortunately where you live is not necessary in Mexico since undercover operations are not allowed.
Hope that helps.