process timing Qs: apply, book biometric appt, get referee signatures?

[pseudonymmed]

I have ILR and will be eligible to apply for naturalisation in a few weeks. I will be going traveling a couple days after so I am wondering whether to apply online before the trip or wait until I return because I am a bit confused about the timing of things under the new system.

If I apply online right away, I understand that right after I have finished the forms and paid, then I will have to make an appointment to go get biometrics taken and scan documents at a UKVCAS centre.

Questions:
-Will they choose the time and place or will I be able to choose a time and place myself?
-Will there likely be many options for dates available?
-Is there a minimum period of time after the online application within which I must have the appointment?

Also since it appears that I must put my referees' info into the form before I can get them to sign, I am wondering...
-would it be a problem to prepare the forms with signature early so that I don't have to waste time after returning from my trip to chase them up on that and potentially delay the biometrics meeting? Or must they be signed after the application is done only?

(I'd ideally like to apply before my trip and book the appointment for as soon as possible after I return, so as not to delay the process. But if I must wait until afterward to get them to sign that would add more time.)

Thanks in advance for any advice!

[CR001]

british-citizenship/questions-on-timing ... l#p1832853