Hi! You mention height restrictions: well please click the link in my signature about LST...it has worked wonders for me....and I didn't even have a height restriction!!! It was still to my benefit though because the yield will be higher.
I say get HPS for best results. You will need good ventilation..fans, even an inline fan plus filter to clean the air. It's SO worth it
Yeah like the others said...be careful with watering!!!! Leaving the plants until they are thirsty is good advice....you will endanger your plants by over watering. What you said about the roots searching for water is exactly right..also you don't want roots rotting at the bottom of the pot from over watering and poor drainage.
Baby Bio LOL
The Canna range is great...but the pro nutrients don't come cheap.
You might like to also click the link to the thread about lighting hours.
Best of luck