I'm planning to refurbish my en-suite bathroom (actually shower room
plus toilet and basin) and would like a shower with a bit of urge -
meaning with a reasonably powerful dual pump to produce a good supply of
(vented) hot and cold stored water. I also want a very low "walk-in"
tray for ease of access as I age. However, I'm wondering whether these
two requirements may be incompatible. Even with a full enclosure, there
needs to be a door - which wouldn't seal well enough to hold water above
tray level.

Are there any rules of thumb for how much flow a shower drain can handle
without flooding the tray? It may be that the only options are either to
go fully "wet-room" with no tray or enclosure, or to settle for a lower
flow rate.

I would like to hear from anyone who has faced similar issues, and to
know what solution they ended up with.
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Cheers,
Roger