Advice needed; best medium for Maudiae-type Paphiopedilum?

[Orchid Whisperer]

I have 2 Maudiae-type Paphiopedilums and one Maudiae (I think) x fairrieanum, I know it's time for a re-pot. I know these are not the highest maintenance type Paphs, but I do want to give them a pretty good potting base & encourage good roots. What I have on hand now is standard coarse fir bark (I can chop it finer to medium or fine, no problem); a little orchiata bark (medium and fine); a mix with bark, perlite and charcoal; and sphagnum (US, not New Zealand).

Need some advice from slipper growers; what medium would you suggest, do I need to but anything different or can I use what's on hand? I mostly use rain water on all of my plants, if that makes a difference. How long would you wait between re-potting now & the next re-pot (I have recently heard 6 months is a good target interval).

Suggestions appreciated - thanks!