I am planning to make a Real Time Strategy game. It will be a 2D RTS, and fairly light weight and completely free. It is just for my hobby.

I have come across the following site

Jose's RTS Sprites

Do you think, AppGameKit Classic can be utilized to build something like that using the sprites in the link?

i haven't seen an RTS in AppGameKit but i'm sure it can be done.

the only snag that i can think of is pathfinding. i haven't seen much on the forums about it beside a number of A* functions (which do work but i haven't seen handling of a number of sprites under it) and i have no personal experience with pathfinding, otherwise.

i do recall someone posting a "fake" group/multiple unit pathfinding example (in 3d i think but it was a 2d design. something about spiders?) but for a decent RTS, there's gotta be a better way.

meanwhile, those sprites are nice. good find. now put 'em to use

Yes it's possible. A* pathfinding is fast enough you shouldn't have any issues with multiple characters. You don't need to calculate a path constantly, only when a unit reaches another square. I did an RTS (unfinished) in DBP and units had formations as well. I did write a pretty lengthy tutorial, but I can't find it on my server at the moment. There are several things you can do to optimize the pathfinding. When in formation, find the path for the formation as if its a single unit. Then each unit just needs to calc a path to stay in that formation (much smaller path, very quick). I had no issues handling dozens of units 15 years ago, never tried hundreds. Kinda depends on what your RTS is like. Warcraft didn't have very many units to handle when you compare it to something like age of empires or command & conquer where you can have hundreds. And A* can work in a variety of maps. Isometric takes no modication, and a hexagon style would take minor changes to take into consideration the additional heuristic directions.

IanM wrote a good A* library in DBP, I ported it to AGK. It was a long time ago, it might need updated. https://forum.thegamecreators.com/thread/206280

This might help you get started. It's for DBP but the thread is several pages and might contain info you can use. I'll try to find my tutorial and get it back online.
https://forum.thegamecreators.com/thread/44248