for sounds, hard to beat SFXR, for pixel art field ... IF we go down the rts path, we can keep the art simple (programmer art works best at the start) we just need to have specs set-up so the art can be changed. (gif or png strips ... 8x8, 32x32...) I really liked DK2, and tried to do a parody rts but dropped it because without good art, all jokes were lost. 2D rts is not to hard to get up and going ... where the problem usually comes in is level design and AI... also tech trees can become overwhelming.
those are high-level problems, but need to be planned out and tested before getting serious...
Solutions abound though. The best way IMO is make mini-games to test game aspects. Start with a demo of unit selection and movement. If multiplayer is planned, here is where beginning testing takes place. Before all the other modules are brought in. At that point you will just know if things are working or not....
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Status of my current game... HexGame with Nucs V2
V1 was completed in GM1.4+ (source code lost .... maybe on older laptop) did not have AI ... Now, I have ideas for AI so I am revisiting the game using JS with multiplayer support via Ably planned ... cool idea to have a JS multiplayer game not requiring a server created using python or something .... Ably was tested using a tic-tac-toe game ... Currently working on the level editor.
The artwork is just boring squares for the units. The game is planned to be almost realtime (very short/adjustable turn times) and limited to 2+ players (+ indicating a neutral player) where the 2nd player can be an AI... The AI will use a simplified MCTS algorithm (tested on tic tac toe 3D on itch.io) so not perfect, but good enough. My hex game currently has 10-14 hex tile types and 5 unit types ... that's it. From a game play perspective, it is very simple. It is all the other stuff that is important.
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I have rambled on a bit here... And games must start with some kind of design document. But, if just going for FUN, there is another way ...
Shall I toss together some stupid RTS thingy (squares vs circles vs triangles) using Ably with crappy sounds just to give everyone something to play with?
Try different art,sounds, maybe even offer multiple control schemes... Nothing fancy, just command a circle to attack a square and see if it does it.... In single player, that would be trivial, but multiplayer via Able with multiple games at once, that is a great place to start and then see if we can make a game out it :)