I use a 5 gallon glass carboy to supply C02 to my 72 gallon bowfront. I have found that it generally produces way too much C02 for my tank, but I have been able to control the rate of C02 production by keeping the temperature of the carboy at or below 60 degrees. The system should be able to generate plenty of pressure to drive the C02 through the diffuser (takes about 24-48 hours to build up enough pressure) so I wouldn't worry about having to pressurize the system. Just be careful to make sure that your line can handle the pressure and your T-junctions and at the rubber stopper on your 5 gallon jug. I use sugar and water up to 15% potential alcohol. (not sure the concentration; I have a hydrometer, they are decently cheap from brew stores).
You might find it difficult to get even flow through all four of your different hoses, especially if your diffusers have different hose lengths and are at different depths in each tank. I would be careful to try and put them at all the same level, so that the C02 does not favor a line with more favorable pressure gradient.
Be very careful about temperature. If your sugar water is brewing at too high a temperature then it will proceed rapidly through fermentation and give you too much C02 too fast, and not last very long. If I keep control of the temp, I can get the C02 to last 2 weeks, but if it gets too warm, fermentation can complete in as little as 4 or 5 days.