Bone heat weighting problem, texture paint problem, blending model Hello fellow Blenders... 

I am attempting to make my first model ever, however I am having some difficulties. I hope you can help me with the following. 

Question 1:

Here is the link to the blend file: 
https://www.dropbox.com/s/cvh9ajtpoxewl6o/leprechaunnotconnecting01.blend?dl=0

I first selected the object, then selected the armature, I pressed CRTL P, Set parent to - armature deform - with automatic weights, however I get the message: bone heat weighting failed to find solution for 1 or more bones. The envelope method seems to work but it lacks precision. When I bow the elbow afterwards, pretty much the entire model moves a bit.

Question 2:
Is it possible to unselect bones for your armature connecting to your mesh? Or does it need to be the entire armature at all times?

Question 3:
As you might have seen my leprechaun has a line in the middle. This is also visible in the 3D rendering software in the game. I copied it's other half. Is it possible to blend out this effect from splitting? So yes, how do I do this?

Question 4: When I texture paint my mesh, it seems to paint on 4 sides at the same time. Is there any solution to this? (try it on the download)

Much appreciated in advantage! Please take into consideration I am very new to this.
This model is very messy. Firstly append it to a new file to fix some viewport messed up settings and make it an appropriate size.



Secondly, automatic weights freak out because of the inverted normal, recalculate them.



Thirdly, clean up weights and pose and reapply parenting.



The model is still a mess 



It is better to take the original and optimize it. https://free3d.com/3d-model/leprechaun-v1--543940.html

Make him T-pose for better results.



Optimize geometry. Better to remesh it. But I won't .



You can also unwrap and bake normals.





The automatic weights are not very suited for this. It might be better to use something more advanced, which is actually intended as an auto rigger. For example https://www.mixamo.com/



Choose T-pose to export



Or paid addon for Blender: https://blendermarket.com/products/auto-rig-pro But be prepared to still fix something manually.

And finally: do not let the frustration beat you 



and have fun 



 Animations from Mixamo