If you're interested in Aglaea, use the Echoes of War

Aglaea is not F2P friendly. She requires premium support to guarantee that she keeps her ultimate up at all times, since allowing the ultimate to drop loses the stacks that accumulated. Also, she is at her best in extended fights. Map exploration and small mob fights isn't going to be exciting. Utilize the support character feature and try her out in boss fights if you're on the fence with her. Recommended fights are:

Harmonious Choir for an easy fight: Everything here is lightning weakness and shares the same hit point pool. The main goal is observing if your team can maintain her energy needs.

Shadow of Fei Xiao for a hard fight: This boss has zero lightning weakness. She drops a huge AOE that you will struggle to withstand since your major damage dealer can't reduce the toughness gauge. This is a fight where even if the main party stays up, the garment maker may lose all its hit points and cause your stacks to drop.

You have three weeks. There is no need to pull day 1. If you can't find a suitable Aglaea to trial run (perhaps you want to try E1), then make a post on the reddit requesting help. I'm sure there is somebody here who would be delighted to friend your account so you can try their character out. Go visit the r/HonkaStarRail_leaks. There should be reliable information on Castorice in the final days of 3.0.

....anything else? Hmmm....be wary of HoYoverse salesmen posing as youtube content creators, enjoy your pulls, and remember that any salt acquired from losing the 50/50 can be saved for cooking. I'm going to wander off now, and hope that I'm smart enough to take my own advice.