To start a new tank, you'd better read the following article:
http://www.aquariumfarm.com/phpBB2/view ... hp?t=61606 To briefly answer your questions:
1. 24" tank is always preferred. It's of larger size that is easier for newbies to monitor and manage the condition of your tank. It's one of the standard sizes that you may easily find appropriate equipment, e.g. lighting system, accessories,... etc.
2. Power Sand Special (基肥) is not a must but preferred. Also, you will need Penac P, Penac W and Tourmaline BC as well. All these will help to keep your tank healthy for a longer period of time. Multi Bottom (根肥) is definitely not required for the first 2-3 months. You'll need them only when your aqua soil starts deteriorating. They simply serve as a supplement to your substrates.
3. For a 24" tank, you can buy a set of T5HO 24Wx4 lighting system. You may turn on ony 3 out of the 4 tubes.
4. The Bubble Counter will not change any pressure of the CO2 system. Since you cannot regulate the CO2 output for a DIY system, you only know how many bubbles per second but have no control over it. For a decent aquatic plant system, a CO2 set is highly recommeded.
5. Chiller is optional, depending on the environment where you place the tank. In winter, there should be no problem at all. But in summer, you'd better keep an eye on the temperature changes. As long as you can keep the temperature range stably within 23c-28c, you may not need a chiller.
My 2 cents.