VERY good idea to start the out of cage time/flying in a smaller room until she has bonded with you and willingly comes to you. You might want to teach her to come to you when you do a certain whistle or ring a bell or something like that and call her name(once she has one lol) It DOES work.
Sounds to me like since the breeder has been letting her out she will already be a pretty good flyer as far as crash n burns go.She's already getting her practice flights and I think that is GREAT. So that part I wouldn't worry too much about. It's the coming to you when she is out that you should work on from the start because like you said with such an open floor plan and high ceilings, if she's not willing to come to you it will be tough when you want her in and SHE is not ready to go in yet.
A good size playstand might be nice to have to give her something of her own to land on and play on while she's out.
I would however still look for danger zones she could accidently fall behind like bookcases or entertainment centers..places that if she fell behind them she would be stuck. THOSE are also places where perch training would come in handy to help her out of a sticky situation...reeeaching her. Perch training would also come in handy to get her from high spots. So yep, work on the perch training too.
If you have everything for the good, balanced, complete seed mix as illusive said I wouldn't worry too much about offering fresh veggies alll the time. As I like to say..IT'S IN THERE! lol
Once a week for vegs will be fine, try to switch it up on what vegs you do feed. Like you said you don't want her going in to breeding mode and holding back on a buffet of veggies offered all the time will help tremendously in that department.
TRY not to worry too much and just ENJOY your new baby when she comes. I know it's hard being a brand new mommy...worrying is what we DO lol But don't let it get in the way of having fun with her. You're certainly more prepared than most at this stage of the game so KUDOS for that
*knockin on wood for you too cyberbud. 4 yrs and no egg laying...yesss! You must be doing something right