I'd have to disagree there. I have an undergravel filter in my 3 ft tank and I have problems with excessive plant growth. I also don't use any additives to enhance plant growth, just fish and light.
For the temp, it really depends on what type of fish you want to keep. I have a community tank with over 16 species of fish (67 all up so far)
I keep the temp at around 26 and it seems to keep all my fish happy, to the point where they breed excessively LOL.
In regards to your pumps, I would suggest holding on to the spare, as you just never know when you might need it. Always pays to have a back up.
With the water, you can add water ager or aqua clear if you want, or you can allow the water to stand in suitable containers for 24 - 48 hours to age, thus not needing any additives.