I’m looking to utilize via in pad (VIPPO) for the first time.  I have some questions for those of you who have done this before.  I’ve got a 0.5mm pitch BGA, with a 0.3mm ball, so I’m targeting a 0.25mm pad.  Now for a couple of questions.
1.  Is there are common way to call out VIPPO on your fab drawing for the board supplier?
2.  Traditionally my suppliers wanted a minimum 3mil annual ring, on a 0.25mm (9.85mil) pad that would mean a <4mil drill, am I missing something.  I thought VIPPO was suited for fine pitch BGAs such as this.  
3.  When I specify VIPPO the via is filled, and plated over, is this done on one side or both sides?
4.  How do I identify which vias should be filled and plated to the board supplier? (I’m using Altium if that matters)
I’m sure to some of you this is old hat, but after all my experience in PCB design I’ve never had a need for VIPPO until now.