In ArcGIS 10.3, If I want to develop a .esriaddin file (addin), is the ArcObjects SDK required? Is VBA still supported, or do I have to develop the addin in Python?
the help files are the best place to start.
if you are referring to developing analysis tools for use in arcmap using python... start here
A quick tour of creating tools with Python—Help | ArcGIS for Desktop
should be looking for web based options, the the other side of the developer divide would best be address by Robert Scheitlin, GISP or Rebecca Strauch, GISP amongst
You might also want to decide upon which side of the developer divide to move your post to given the structure of GeoNet as outlined here GeoNet Community Structure
By tools sets, do you mean something like a python addin? That is, something you can easily package and distribute? Just in case it is....
What is a Python add-in?—Help | ArcGIS for Desktop
Here is info on addins I have included in a blog Tip: Python Addins - getting custom tools/toolbox to work - GPToolDialog error and other tips (9/7/2017)
for what it's worth. Keep in mind that all though toolboxs will still be able to be used in Pro, if you go that route, as least for now, addin will not.
Retrieving data ...