Honestly dont even think about Ancient Power. Forget that this is even in the game and enjoy the way it is. Climb as high in Onslaught as u can, farm ur shards together, finish Mastery Mode for the awesome Destructive Pylon and Automation shard and after that you can consider the AP reset.
When you reset, all your shards that arent gilded will be reset to 0, all gear (equipped and in storage/inventory) will be reset to campaign lvl and you will drop down to your current minimum ascension. If your reset to early, you will lose interest in the game quite fast, cause you might end up back at zero, but with enough preparation, you can actually go from peasant to demi god :P
Overall most people would recommend doing your resets after you managed to beat at least Onslaught F100-120 sou you will be at around 1000+ minimum ascension. Others recommend or try to climb to F273 for a minimum ascension level of 3060+ and a full ascension cap of 999 for defense power and so, which would net you a bonus of 19980 Defense Power for free on the skilled defense. This defense power bonus is higher than getting a c7 10/10 relic to c8 5/5!
So overall, take your time and enjoy the journey. No need to rush things