How to politely negotiate working conditions/expectations in an ongoing advisor/trainee relationship?
I think you should absolutely have a conversation with your PI.  I also think that you can discuss your needs in a mature, polite, and straightforward way such that there is no ultimatum and no negative feelings.


Step 1.  Email your PI requesting a meeting for this discussion specifically. "Hello PI, As you know, I have to make a decision about transitioning into the PhD program by March X.  I was wondering if you could meet with me to discuss this. Thanks, Azzzzzz." This will eliminate the surprise element regarding your conversation with her about these non research related things. That is, if you unexpectedly brought this all up during a regular meeting, it could catch her off guard and lead to a less than positive outcome.
Step 2. Be open and honest with your PI. But do so in a way that leaves room for your PI to be the mentor.  That is, your post has several hints of arrogance and also suggests that you are really worried about there being a potential for confrontation. That is not the right mindset.  You need to focus on what you both want. Your PI is a mentor, and as such wants the best for you, but you have to actually allow her to mentor you. The tone of your conversation should not be: "I need this and this," but instead, "I'm concerned about my growth in this program and so I want to get your insight about these things..." Be open and honest and humble. Keep in mind that you are on the same team.
Re: continuous guidance. Ask your PI to schedule weekly or maybe 2x weekly meetings with you. This way you have a dedicated timeslot with her regardless of how busy she is. Again, do not present this like, "I want weekly meetings," but rather, "one thing that would really help me is if we could dedicate a time for weekly meetings." 
Re: constructive feedback.  I once worked with an amazing PI who would often withhold feedback. But a trick I learned is that if I asked them, "Would you do it like this?" or "What do you think can be improved on XX?" Once I specifically asked, they gave it to me! I appreciated that I had some independence to make my own mistakes and learn from them, but at the same time, whenever I needed a little more guidance I just had to explicitly ask for it.
Re: constructive feedback (part 2). In addition to using the above method in a more day-to-day kind of way, you could also just tell your PI that you want more constructive feedback. Your PI sounds pretty open to suggestion.  It's entirely possible she doesn't know that you feel like you aren't getting enough. Have this meta conversation with her. Again, frame it in a way that does not point fingers at her for not providing it, but instead in a way that humbly asks for more of her input so that you can grow.


This really shouldn't be just the one conversation.  You should use this initial discussion as a starting off point where you can be more open and honest about what your needs are and what expectations your PI has. When something comes up address it sooner than later, don't suck it all up with a smile--no one benefits from that. 

A final thought is that if you are harboring thoughts related to pay and job offers while in a PhD program, it's possible that pursuing a PhD is not the right fit for you. Even more generally, thinking about "what could be" or "what if" seems unhelpful at best and detrimental at worst. Still, having these thoughts might be a hint about what is the best decision for you.

I hope this helps. Best of luck.