- When planning to self-publish a game, which is the contract model to be followed is the same offered when it will publish a game for hosted games?
When you do it yourself, you pay COG 25% and the Platform (Apple, Google, etc) 30%, and keep the rest. You have to put it up, which incurs a small fee and some know how.
Hosted Games pays 30% to Platform, 25% to you, the rest to COG, but they put it up on all markets.
The order of these percents changes the final totals.
- The choice of games is california, how the contract for foreigners? What is the constitution to be taken into account when entering into any contract, the US? Another thing that I believe is relevant. As the choice intend to deal with WHAT was raised? By paypal? If this logic, the expatriation of what was collected is assumed responsibility of the author?
Canada has a Tax Treaty, as do many other countries. This stops double taxation. As to the mechanism of payment, they’ve switched to another system with lower fees and currency conversions built in. Unfortunately, I forget the name. Again, available in most countries. Each country is different, you’ll need to see what your country has set up. Yes, in Canada, I pay full Canadian taxes on what I make.
- When it is said that the choice is 25% and the author gets 75% of WHAT it is applied? The total collected indefinitely? As these progressive discounts, depending on the case, retroactive happen?
Platform first, then COG, then Author… 100(0.70)(0.75), so you get closer to 52.5% when self publishing. Payments are about 2 months behind actual sales. If your pay for the month is less than $100, they save it until it reaches that threshold. Checks should keep coming as long as people keep buying. 
- The choice games have any problems using steam greenlight to self-publish a game?
Steam is a difficult market to be allowed into. CoG has had to build credit with them and is unable to put all there games there immediately. I don’t suspect that a self-publisher would find it any easier.
- It is possible instead of the fee (25% -75%) pay a single fee (albeit high) for use of the permit?
You’ll have to discuss specific terms with CoG.
I hope some of this helps. Disclaimer: This is from memory, things change, and I have no CoG authority. So, you’ll need to check specifics yourself.