Planted Tank Guru
Join Date: Sep 2006
Location: Northern California
Hey there Mark,
Glad to see you've done a bit of research already, before asking your questions.
What plants are you trying to keep?
1) Fixture 1 has 65 watts of PC lighting. Fixture 2 has only about 36 watts of T5NO. Even though one is PC lighting (less efficient), it'll still be more light than half of it's wattage equivalent in a T5 fixture. Having multiple bulbs lets you pick and choose to see if a combination suits your eye better than a single bulb. Is it crucial? No.
2) I wouldn't think a glass lid would be necessary.
3) Yes, a HOB filter will outgas your CO2. An internal filter might be OK if you find a way to prevent shrimp from getting sucked into there. I recommend scouring Craigslist for deals on a canister filter. An Eheim 2215 or Rena Filstar XP2 will do you well on a 20 gallon tank.