From personal experience,
1. Raccoons ate my fish from the hospital tote behind the pond garden, but never from inside the pond. since yours is only 700 litters, you may need to protect against raccoons or other similar animals in your area.
2. Frogs will be inevitable, I have a nice stock of venestus cichlids that keep it egg/tadpole free.
3. Egrets are my biggest enemy (lost about 30 fish). I ran really thin fish line around perimeter and across the pond leaving 1-2 feet space between each wire. This solved the egret situation. You can see a few lines in the photo.
4. never an issue with cats and dogs.
5. As for cold days/nights, I'm in Miami, but on rare cold nights, I never noticed an adverse affect but I do have a 1500g or more pond. 3-4ft deep.
6. I do run heavy air pumps and as a bonus, I have a waterfall and a filter outlet which creates major surface agitation.
As for pumps, I use the readily available Home depot or lowes pumps; around $250each. I use their 3200 hpg fountain pump and built a custom filtration using 2 x 55g drums. Prior to this, I ran two pumps to a canister filter each. I'm currently running a UV light in the second drum which contains the sock filtered water. I can honestly say that you do not really need a UV light once you get proper water conditions.
Since you're only 700 liters, I would go with two cheap canister filters and dish out the idea of the pumps. I just bought a sunsun hw3000 for $120; you can buy two of the $85 ones to make it budget friendly. I have a huge water fountain in my front yard full of shrimps, guppies, mollies, angels, guramis, etc. You name it, I got it. I dug a 1-1/2 to 2 foot hole and put in an oversized bucket in it. I placed my sun sun inside the bucket and ran the in/out lines through a lid. you can't even see a filter running my fountain.