Understanding the sequence of events associated with ILR Standard Service

I had a few questions pertaining to the overall sequence of events associated with Standard and Priority ILR appointments from within the UK -- knowing that Priority appointments are currently not available:

1 - Am I correct that the biometric appointment associated with the Standard service (and with the Priority service, should it become available again) must be made at a UKVCAS service point, rather than a Post Office branch?

2 - Am I correct that when attending my UKVCAS appointment, I turn over my passport and BRP to UKVCAS at that time, and will not get them back the same day? Should I expect that it may take a long time for my documents to be returned if I apply Standard (and if so roughly how long)?

3 - Regarding "you should NOT travel outside the UK while your application is being processed or else your application will be considered automatically withdrawn" - does an ILR application start being "processed" immediately after submission? Or is travelling outside the UK alright as long as it is done before the biometrics appointment?

Apologies if this is the wrong forum, I figured this is the place since I am asking about the ILR standard and priority services specifically, but if this needs to be posted in the General UK Immigration forum I can repost there.

Thanks in advance.

1. All biomtric appointments are with UKCVAS. The priority or standard service is a UKVI service, not a UKCVAS service.

2. NO original documents are submitted. You simply take them with you for identity check and you get them back. UKCVAS is a third party agent for biometrics only. They are not UKVI staff.

3. You should ideally not travel as your application could be considered withdrawn and lose the fee paid.