Just remember, if you have the plugs under the tank they will get wet in case of leaks, splashes etc. A surge protector won't help if the plugs are flooded. Besides, you don't want a surge protector, you want an RCD.
6 plugs will easily be used
1. heaterstat
2. lights
3. filter
4. pump for additional bubble wall you decide looks cool
5. 2nd heaterstat for safety
6. 2nd filter (small internal to keep as standby