Not enough info to recommend things really but some thoughts -
You need the pump to circulate the water at a rate dependent on (typically) the amount of fish it contains. Normally you'd want to circulate the water in about 2 hours for a modest amount of fish. The amount of water a pump handles depends on the height it needs to raise it. Typically for your 2 tiers you'd need to raise it no more than 1 metre or a good bit less so for your 1000 gallon pond you need a circulation of around 500 gallons per hour at a head of 1 metre. Manufacturers are pretty optimistic and there are losses in the piping and when the filter is dirty so somewhere around 800 gallons/hour nominal would be a good target. Not too much more or the water will rush round too much. Note that the distance raised is measured from the surface of the pool it is pumped from to the highest point in the system no matter where the pump or filter are.
There are umpteen pump makes on the market. I always use Oase who are not cheap but are definitely long-lived and not prone to much bother. You need a pump which won't block easily. A possibly suitable one is the 'Oase Aquamax Eco Start 5500'. See here
http://www.aquatix-2u.co.uk/acatalog/oase_aquamax_eco_start_filter_pumps.html for instance.
If you want the filter outlet to be below the highest water level then yes it will need to be a pressurised one. If you are having fish (and probably in any case) you want one with a UV lamp to help keep the algae etc. down. The pressurised ones are all much too small for the volume of water they can supposedly filter so you really want to get one which is about twice as big as the blurb recommends (and even then it will be too small). Possible makes are Hozelock or Fishmate - you could think about a 'Fish Mate Powerclenz 15000'. See here
http://www.aquatix-2u.co.uk/acatalog/fish_mate_powerclenz_pond_filters.html for instance. I would really recommend an oversize one to reduce maintenance but they're much more expensive of course.
You can get cheaper ones which are similar to both the above. In my exerience pond stuff like so many other things doesn't repay cheapness.
Other thoughts:
The filter will need cleaning regularly so it needs to be accessible. Some (like the above) have semi-automated cleaning mechanisms which work after a fashion but you should reckon on needing to open things up and clean out at least every 2-3 months. Note that the pressurised filters are usually much smaller than an 'equivalent' non-pressurised one and gunge up proportionally often. They're more awkward to clean out too.
If you want any sort of fountain (I wouldn't because it will forever need cleaning out) it is very difficult to achieve with the same pump used to drive the filter.
If it looks or sounds Chinese run away. Sadly most of the filters including the above are usually Chinese made (and Oase is really too expensive).
Fish - particularly Koi - grow quickly.
