The trapping mechanism of pinguiculas is relatively simple compared to other carnivorous plants (eg. venus fly traps), as they basically act like sticky fly paper. During their growing phase (Spring - Autumn), the leaves of Mexican pinguiculas will produce enzymes to catch and digest insects. Washing their leaves with water will dilute and remove these enzymes, which the plant will then need to regenerate once again. For this reason it is best to avoid getting water on their leaves, especially during the growing phase. 

Pinguicula do prefer higher humidity and warmth during the growing phase, but in winter they should be kept cooler and drier. Most will start to hibernate as the temperature drops, and will produce smaller,  more succulent type leaves. The temperature fluctuations typical of the common house in temperature Australia will be sufficient for Mexican pinguicula to cycle from their growing phase into hibernation. Household humidity is also sufficient for pinguicula. 

During the growing season, I keep my pinguicula growing pot in a tray with 1-2 cm of water sitting in it. It’s very easy to just keep the tray filled with water and replenish when you see it’s empty. They don't like to dry out, but can still experience rot. For this reason, I occasionally leave the tray dry for a day or two between waterings. The rule is to keep moist-damp during the growing season and in winter, hold back on the watering and only keep moist. Do not keep the tray fill of water in Winter, as you will rot the plants. 

Its best to utilise rain water (or deionised water) where possible, but I have had no issues using tap water in Melbourne. If concerned, you can leave the tap water out it for 24 hours before watering, as the volatile chemicals in it, such as chlorine, will evaporate. Of course ensure your local water isn’t hard, otherwise you’ll definitely need rainwater. Also be very cautious with fertiliser. Many fertilisers will quickly kill your carnivorous plants, so I suggest avoid using them all together. 

You could repot pinguicula anytime of the year providing you take care not to damage their shallow roots, although I would suggest preferably repotting during the growing season, or immediately after hibernation. This would give the plant greater chance of recovery if any damage was inflected to their roots during the process. 

Generally the roots of pinguicula act more as an anchorage than anything else, and I’ve snapped off roots before without too much dire set back (I don’t suggest you do that though). You can repot into sphagnum, perlite, peat moss, coarse sand and I’ve even seen people grow them on limestone. For simplicity I just use sphagnum, which can also be mixed it with some perlite to reduce costs. It’s been said that they prefer alkaline soil, but I like to keep it simple and not bother too much about the PH. They grow well for me in an acidic soil, so I’ll keep it that way.

Don’t unless you’re an expert grower and want to test. However if you do catch gnats and have squished a few, definitely feed it to them. They’ll digest them for you. They usually will catch what they need. Good luck in growing your pinguicula. I hope you love them as much as I do.