Go slow, learn about growing plants before you plunge head first into a high light tank. Starting out with 4-5wpg is a surefire way of quitting the hobby, talking from experience here.
At 4wpg you have very little room for mistakes. Consistent CO2 is a must, the DIY method won't cut it. Ferts on a daily basis is a must, you forget a few days and algae will become a major problem quickly. Lighting is only one part of the equation to plant growth, you skimp on the others and you're doomed to fail.
You can have a nice tank with 2wpg. Want an ADA iwagumi setup with lush groundcover? Entirely possible with HC, dwarf hairgrass, marsilea, or E. tenellus at 2wpg. Want red plants? Also possible with around 2wpg. Growth will be slower, but demands on CO2 and ferts are also less.
Plants grow best at around 70-85 deg, if your room dips below that then get a heater.
1. Substrate. ADA Aquasoil is best. It's nutrient rich, moreso than any other substrate out there. Flourite is decent, better than plain gravel or sand. Comparable to Flourite is Eco-Complete and Onyx Sand. There's Schultz Aquatic Soil used in home gardens, which is a little better than Flourite.
2. Its a good idea to cool overdriven lights, will prolong the bulb life.
3. CO2 is an extremely important part of growing plants, it's the other half of photosynthesis. If you want to grow a wide variety of plants you're going to need CO2. The DIY yeast method is only really suitable for small tanks with low to moderate lighting. You need pressurized if you want high light.
4. Ferilizers are important. Plants need their all of their nutrients in order to grow. The more light the higher demand on nutrients.