I think you are more or less on the right lines already. First law of BDSM - communicate. If you do that right then everything else will follow because knowing what you are doing right and wrong is essential for a Dom. So, the first girl you need to chat to (out of 'character' so you are not her Dom and she is not your sub) about what you asked her to do before. Did she enjoy it? What didn't she enjoy? You can then use this info to feed into your planning for next time.
Girl 2, I think you need to take it slow and try not to scare her away. An option may be to talk to her about fantasies and direct her to websites that may answer some of her questions or stories that contain her fantasies. I would be very adverse to trying to persuade her, by any means, to to anything physical as that can have the opposite effect - causing her to pull away. Instead, make sure she has all the information she needs and, when she is ready, she will come to you.
I also think you need to make sure that both girls are aware that you are talking to the other and 'having internet sex with another girl'. It may not seem like such a big thing but many people see even the internet thing as being the same as actually having sex with someone. If you are open and honest about it now, it leaves you with more open options later (maybe they are both ok with it, in which case 'win'maybe one would like a more serious committment and want you to leave the other, in which case you can do that with a lot less fuss than if you were sneaking around).
If you want to keep it up online (and I am assuming here that she lives far enough away that real life is not possible?) then a webcam is a good investment for both of you. Also, some form of voice messenger system (VOIP) like skype or using the microphone on yahoo messenger. The VOIP thing is useful because it allows her to hear your commands and respond verbally while performing tasks. If she has to take off bondage everytime she wants to 'say' something (like beg for an orgasm) then it takes away some of the feel of the session. Also it is more rewarding for you as you can hear her responses.
You might also want to consider sending tasks over e-mail and, if you have access to it, text message to her mobile phone. These two give you a level of control in her everyday life, not just when she is in a prearranged session with you.
Finally, in the absence of webcams, consider using a digital camera to photograph or video her completing tasks (most these days have some form of timer on them).