Open rtsTemplate.capx with Construct2, this is the source of the template with comments and code is well structured using groups. Easy to customize. A long time ago I know that this template was compatible with Construct3, I cannot confirm that this template is still compatible with Construct3.
Included : touch screen support for mobile, minimap, build base and units, multi-selection, pathfinding, AI build some base and units, ressource management, upgrades. You can try the free online demo of the template here.