The Blue Sun Mod

[JackintheBox]

--When outside borders in Global map; a message sometimes appears saying "We have a chance to ambush 19 Bandits"
I enter sector and there is never anyone there?

Yes they are there and there are no yellow circles at the start. What happens is that you will get placed somewhere on the map, and the bandits will spawn were the yellow circles normally would be. They just stand around and battle starts when they spot you, or when you open fire first. Which you should

--After using blood packs and blanks to pretend to shoot Barrea in Tanya's camp, going back to Artigo it says I killed him instead?

Sure you actually loaded your gun with the blanks?
It is not enough to just pick them up, and the gun you get from Tanya is loaded with live rounds.

--After shooting Tanya's man Gorrzo? In Sagrada and not lettting any of his men escape, Artigo says it was a Failed mission?

I am not really sure what mission you are referring to.
Could you clarify it a bit more?

--The mechanic in Blue Home Base camp doesn't upgrade any of the weapons on his list the only options that appear are
Back, end conversation. Even if I have a DVD... I mean SVD in my hands.

You need to give him the weapon manuals you can find around the country. Otherwise he can not perform the upgrades for you.
Every upgrade choice has one manual out there.