Hello and welcome.
If I get a plant from someone I don't know I knock it out of the pot to check the roots. Paphs don't seem to mind.
My roth generally blooms at 16-18 in. leaf span. I don't really know about the sandie but I seem to remember someone saying the LS needs to be about 20 in. Some one who grows phrags will hopefully chime in.
Here's a pretty good site for climate info: Paphiopedilum Data Sheets