Nice, that's a lot of filtration. Interesting that you're using a 300 watt Hydor. I was considering selling mine because I thought it would be too much for the smaller tank and overheat. Will def. be following this thread to see how it goes!
Yeah, the 300 watt heater was only slightly more expensive than the 250 watt version. No brainer when I purchased it. Also, I was living in Michigan and the winters were BRUTAL. Plus, a bigger heater simply means it comes on less (it's temperature controlled, so it stops/starts automatically).
As to the filters, I first started out wanting to put powerheads in the tank. Here is what I considered:
Powerhead PROs - Cheap, Reliable, Very Low Maintenance, Good Flow
Powerhead CONs - Takes Tank Space, Visible (ugly), No Added Filtration
Canister Filter PROs - Invisible, Added Filtration, Average Flow, Redundancy (when changing/cleaning)
Canister Filter CONs - Expensive, Maintenance, Space at bottom/next to tank
I originally had the Eheim 2215 for a 46 gallon bow front. The flow was average. Then, I got a good deal on a used Eheim 2217. Instead of getting a separate powerhead or external pump to power my Mazzei, I used another canister. Problem solved! Plus, you get all the benefits listed above. If the price is right, get another canister (or get 1 powerful external pump and a sump).