Beginner looking for a little guidance

Greetings all,

 I have decided to give making an indie game or two a shot over the next couple of years.  I have UE4 and Blender ready to roll and I have been messing around in them for about a week.  I really do not have a clue as to what I am doing yet but I plan to learn.  Just a couple of questions to try and save me some headaches, if anyone feels they can provide some good advice.

 First I am teaching myself C++ and plan to learn C# after that.  Trying to learn Blender as well so I can build some assets.  Plan to use UE4 as it seems easier to follow for me compared to Unity.  The goal is to make a military game, an rpg, and a zombie survival type game.  I got some really cool ideas. (Like a lot of you do as well I am sure!).

 My motivation is to have fun learning and make something friends and gamers alike can play and enjoy.  If its financially rewarding then great, but that is not my main motivation.  Best case scenario, my games do really well and I start a small studio and expand it to triple A titles in 5-10 yrs... then I can quit my day job.

Here are my concerns:

  When building models in blender, are there specifics sizes I need to create so they look decent in UE to avoid having to rebuild them?

  What is the work flow? for example: I have all my ideas pretty much mapped out with wiggle room should something come up along the way.  

  Should I be focusing on creating assets like weapons, characters, vehicles or should I build the worlds first? 

  Do I do all that(graphics) before I code or should I try coding with a placeholder, like just making cubes bounce across a stage and go back later with the final models and swap 
  them in?
  Is there any suggested tutorials or concepts I should be digging into to prepare for the future of the project?  I can spend about 2-3 hours a day working on projects,                      
  so I expect to put 10-15 hours in a week be it reading, trial and error, testing etc..  

  If there is anyone who would like to be a mentor that I can shoot an email when I get stuck and can't find an answer to that would be great.  I live in Texas, so people in the              
  U.S. are preferred only because of time zones.  But as a gamer, I have met plenty of people from all over the world so I can be friends with anyone.  

  Thank you all for taking time to read this and provide any tips or suggestions that might help myself or others reading this thread.  Your knowledge and consideration are 
  greatly appreciated!

   -That Nerdy Rascal

If working alone, you should definitely start with designing and implementing the game mechanics. The game you end up with could be very different from what you first envisioned, so art created early risk being unusable.

You have a lot to learn, so I recommend saving C++ for later. You can create games in UE4 without using it at all.

Learning C++ is a major task on its own. Then you need to learn how Unreal Engine uses C++ which is another major task if you want to get your hands on all of it. If you already have experience with programming it obviously helps a lot.

C# you can skip if you want to use Unreal Engine. You may even skip C++ in the beginning and stick to Blueprints.

Your idea for a game needs to be put to the test in a prototype as quickly as possible so you can adjust or discard it if it doesn’t work. It is the foundation for the game so the models can be placeholders and exchanged in the final stage.
It is common for beginners to have overly ambitious ideas for a game so you should probably start by focusing on only the essential parts of the game in order to be able to finish the game.