HOB filters take up surface space on a tank, where you could have lights. (i.e - canisters filter take up no extra space in the tank so that space can be filled with lights)
Here are some pages I've made with info on CO2 tanks, DIY reactors and I am working on regulators now;
IMHO you should not try to use DIY on more than a 40g tank. In the end it is too much of a hassle for the result. Tanks ar ean investment and as you get into bigger tanks it will cost money to get things going. You can put pressurized CO2 on a tank for $100-150. Most of the expense is one time. After the initial investment you can add as many tanks as you want for just a few $$ more.