Hoping others will jump in here, I'm not actually experienced enough to know how to answer you. I have all 55 watt bulbs. I can say that 4 x 55 watts on my 59 gallon tank is too much I think, at 3.7 wpg, and I suspect that 2.7 wpg would be OK.
As for DIY CO2, while 30 gallon is often regarded as the upper limit, a larger jug like a Gatorade jug and provide more gas, and you can use two bottles as needed, so I say go for it. The better the reactor, the more leeway you have. I use a PowerGuild internal power reactor in one tank and a DIY copy of it in another. If you don't mind internal equipment, it works great. Easy enough to spring for a tank and regulator set later as the cash is available. Or keep your eyes open for someone sellling used equipment.