1. If you request constructor, the starbase will find an idle constructor and tell it to move to the starbase.  If there is no idle constructor, it will then ask a nearby starbase to build one and send it over.  This is a handy button that takes a few steps out of upgrading starbases.

2. You must build the appropriate building for the bonus type if you wish to get any benefit.  Tourism building for a tourism bonus, etc.

3. As you research more techs you'll get some Military buildings like Military Academy or Hyperion Shrinker.

4. Currently working as intended.  The developers might tweak the rules to make diminishing returns on stacking sensors.

5. Yes, in expansions and DLC.

6. Yep. Documents/My Games/Galciv3/Designs is where I find my ship designs.

7. (can't answer, I don't do multiplayer)

8. I am not sure what you mean.

9. Starbases affect tiles that are up to 5 tiles away from them.  Certain mid-to-late game techs can expand that area, allowing starbases to mine further away.  It is not in any way dependent on your influence, as you can use starbases in other people's area of influence (though they won't like that!)

10. Tourism is automatic - you don't have to do anything to activate it, it just adds income to every planet.  Trade, you build a Freighter, then send that trader to a foreign planet.  Once it arrives, a trade route will be established and generate income for you.

11. The planet screen shows your total population and your total food.  Food is your population cap - if your population equals your food, your planet will not grow in population.   If it is under the cap, your population will grow.

12. I think you understand prototypes, you just didn't have the resource you think you did.?  I've done that before.  Each prototype component requires one resource, and some buildings require those too.  So if you put 3 Durantium Drivers on a ship, you need 3 Durantium for that.

It should be noted that Tourism doesn't start happening until you research Interstellar Tourism, unless you play a Wealthy race, in which case you start with tourism enabled. Once active, tourism just works.

You send another constructor. Hence the "request constructor" button. Helps the process.

And improve/build modules on the star bases.

That's exactly right!  Or you can click "request constructor" to have the game build it and move it for you.

10 - So you build a "freighter" and send it to a planet from a different race?  There is no trade inside your empire? Also if you send a 2nd ship, doe that increase the trade?

11 - The greater the difference between FOOD and POPULATION = population growth?

I don't know if the growth depends on the current population or that difference, or if it is just constant...however, I do know that if you end up over the population (maybe food was destroyed or you transported population from another planet), it will decrease over time....

I think the pragmatic Preparation Center also utilizes that trait...

If I recall correctly, you can only have one trade route between two specific planets. So I think planet A can have routes going to B, C, and D, but not two routes to B.

There is a stat that limits how many trade routes you can have in total - Trade Licenses, or something like that. Various techs and other things can increase it.

Part of the value of a trade route is calculated based on the income produced by the two worlds involved.  So you want to select one of your worlds that has a good sized population and perhaps some wealth buildings (and trade buildings if you've researched them) and then look for an AI planet that also looks rich and is as far away as you can find.