Sounds like an adventure, but don't be afraid. DIY CO2 is easy and fun
<<1. I want to do something cheap and easy since it's a temporary fix. I have a 1 gallon plastic jug with a screw on cap, airline tubing, and a check valve. My thought is to run the tubing into the intake for my filter (Penguin 330) so that I don't have to get a ladder. Will this work okay?>>
If you get all connections tight, it should work. You will need to keep track of pH, to see if the CO2 gets dissolved into the water and not outgassed by the Penguin.
<<2. Can I use one of the 2L bottle recipes on here, or will I need to add more yeast and sugar for the gallon jug? >>
Yep, I would use two cups o' sugar instead of one, and a little more yeast, maybe half a teaspoon, although it isn't that critical.
<<3. What's the best way to get the tubing going through the neck of the bottle? Drill a hole smaller than the tubing and cut tubing at an angle to force it through? Drill a hole roughly the size of the tubing and use silicone sealant? I also have a rubber stopper that goes over a 1 gallon jug mouth for wine/beer brewing purposes that I could use, but I think the rigid tube that goes through that is a larger diameter than airline tubing.>>
Either one... Silicone sealant doesn't bond so well with tubing, so either you use some sort of plastic nipple and glue it in, or use the smaller hole / pull airline through sort of deal. Rubber stopper sounds good too, maybe you can soften up the airline and get it over that rigid tube.
<<4. Would a one gallon jug rigged up in this way, running through a bio-wheel-type filter produce enough CO2 that I'd have to worry about my fish at night? Should I run an airstone? Unhook the CO2 at night? Buy a GH/KH test before I think about doing this? (I have a PH test kit.) Or should I just wait until I get my lights and my Red Sea system?>>
Nobody can tell you, you just need to know the kH and keep track of the pH and see what happens. I'd say that you don't have to worry at night, and should worry about getting CO2 into the water at all with the biowheel.
<<I was just thinking about giving this a shot today and wondered what advice/warnings/tips I might glean from the DIY folks. Thanks for any ideas you might be able to share.>>
Just start slowly, read a lot because most ever possible problems have been discussed here