Phil, if you can...I would run a dedicated 20 or 30 amp circuit from your main power panel to the room that your tank is in and I would also use 10g wire depending how far the run is from the main power panel to the tank...but no less that 12g. Normally there are many other outlets connected to what every circuit you are going to plug in the tank to.
The 100A main Service will be fine as how much do you have on at any time in the house...but you might find that you are tripping the breaker if you have other high amp draw items on the same circuit as the tank...The room my 120 was in with the two 250w MH and the two 110W VHO's was on the same circuit as my kitchen outlets...there was no way that the circuit would run the tank and coffee maker or microwave at the same time...so I ended up running a dedicated line from the main power panel to the room with the tank...
don't forget to install a GFCI in the circuit...the best would be to install a circuit break at the main power panel that has a built in GFCI..ask me how I know this! LOL..I had a cooling fan get salt build up in it and started tripping the GFCI I installed in the outlet itself (like the ones you see in your bathroom) and what a pain it was to reset the GFCI when it was behind the tank...I could just barely reach it with my fingers to push the reset button...so I really wish I would have spent the money on installing a CB with the GFCI installed in it...little more money...but would have been a whole heck of a lot easier to walk to the basement and reset the GFCI at the main power panel...than to become a contortionist trying to reset the GFCI behind the tank.
I have an electrical background...so I made sure I was doing everything to code...but if you aren't sure...I would hire an electrician to come install the dedicated circuit...
Just my two cents on the subject...as you are going to be pulling a lot of amps through that outlet...as you said...around 10A just in lights...not to mention heater/ chiller, pumps, etc...very easy to be pulling 15 or 16 Amps through the circuit during the day with lights on and a chiller running....