If your tank is 400L, I would say 8,000 LPH is your minimum. You ideally should shoot for more, but most DC pumps would do that. The turnover or total flow rate for the tank should be total between all powerheads. I personally like to split the flow between as many powerheads as financially and logistically possible because it gives you options in terms of tuning and directing your flow intelligently.
If you're going with Jebaos, I would purchase the OW series. It's the most recent series and purports to offer several benefits over previous generations. The OW-40 offers about 15,000 LPH of flow. This would be more than sufficient for your tank. I would at the very least get two pumps and position them at either ends of the tank, pointing toward each other. In the random flow mode, this will create pretty good flow.
Many people complain about the quality of Jebaos because they don't last as long as a Tunze or Ecotech. But remember that they're a quarter of the price of these more expensive pumps. Expect reasonable lifespans of a year or two (my Jebaos are all passing the 2 year mark soon), but also be prepared for some failures. These pumps are priced to account for this.
