Automatic cleaner for swimming pond

Hi,

I've just finished building my swimming pond (50 m3 swimming area with 13 m3
biofilter with lava rock). Construction is concrete brick walls with EPDM
rubber liner.
Since it collects quite some debris (leaves and stuff) which sinks to the
bottom before the surface flow drives it to the biofilter, I will need to
clean the it regularly.
I'm therefor planning to install an automatic cleaning system. My 'pond
contractor' suggests to use a Baracuda G3 with dedicated pump (can't use the
biofilter pumps) and a dedicated 150 liter lava-rock filter.

Any experience with such a setup ?
How should the pump be rated ?
Do I really need the extra filter? The contractor believes that if I only
use my biofilter, the fine debris will eventually clog it. If so, wouldn't a
smaller filter or even the Zodiac leaf catcher suffice?

Thanks in advance.

Koen