Um ohk where do i start. If i was you and was going to do a 450L planted i would use more than 4 t8 tubes. I would look at using around 6 if you are going to go seriously planted, and have co2 and stuff. As quack said, don't bother about DIY co2, i found it so annoying to mix up new batches, and the margin for error is too much of a risk as you cant control the amount of co2 very accurately. Reef is selling a brand new tunze regulator on trademe ATM that you may be interested in, I just bought one exactly the same off him but it was older. They are quality regs. BOC rent out bottles for $11 a month, and a fill is only $30, and that should last you for over a year. If you are going high tech, and have the extra $$, then sure, use under gravel heating, but IMO, it is just as extra unnecessary cost that you only need if you are VERY serious about having a mint planted tank. I don't have undergravel heating on my 250L planted and i can grow any plant i want 8)
HTH