Your tax-income.

There are two ways: increasing your population or increasing your influence.

The total amount of tourism-income generated depends on the population within the galaxy. Each billion people generate a certain amount of bc, but I don't know the value. The share every race gets of this money depends on their influence. For example, if your race produces 30% of the influence in the galaxy, you will get 30% of the tourism.

A higher population also means more influence and more taxes, making this the more lucrative way. However, a higher population also means, that your approval-rating will be lower. This will bring its one share of problems.

There is also a UP proposal and a couple random events, which will increase tourism, but they are not guaranteed to appear.

If you give the research treaty to another race then they will get 10% of your total research (or you from them, if you got their treaty). You don't loose the research though. Sharing your treaty also increases your diplomatic relations with that race, making it easier to get an alliance with them.
However, there are some downsides. The first is, that you can share your treaty only with one race. The second is, that, if you declare war on a race you're sharing your treaty with, you'll get permanently branded as an untrustworthy bastard by everyone, which can make diplomatic negotiations pretty hard.

Yes, just keep them away from combat, and your ships will repair themselves. However, the speed at which they repair is pretty low. You can improve it by increasing your Repair ability and placing the ships in orbit of one of your planets. It will still take a long time though, if your ships are heavily damaged.

There is a faster way to repair ships, but it is technically an exploit. If you don't like exploits, then just ignore this paragraph. The game has a upgrade-mechanic for ships. Using it will also repair any damage. You can't upgrade a ship to the same design, but there is an easy way to work around it. Just make a copy of the design and call it something different. You can then switch between the designs each time you want to repair the ship.
Upgrading ships has an opportunity cost in form of money and time. Money won't be a problem, because using basically the same design will cost you only a pittance. Time, on the other hand, could become a problem. The further away your ships are from your planets and starbases, the longer it will take to upgrade them. Extremely important to note is, that your ships will only have 1 HP during that time. So guard them with your other ships.

How Do I post a question in this forum!!!!