You know, I just had the same question/issue as you. We probably had a similar-sized galley and had the same issue with joist right where we wanted to put our cans. I wish I could give you a definitive answer... but I can't - we ended up installing only a single row (also, not ideal, but we're happy). The contractor might have forgotten or maybe it was because he felt they would be pretty close. If they were placed 32" away they'd be about 21" apart rim to rim which felt too close to us (others may disagree). However, I have seen photos of people who installed lights even closer and they have seemed more than happy with them. You should still have 5" clearance to the rim.

Landscape light sockets take a lot of water abuse and sometimes don't make good contact with the lamp connections. Designs of newer better quality fixtures may have glass shields to protect the socket & lamp. Landscape lighting installers often do yearly maintenance on fixtures replacing lamps, applying a corrosion inhibitor and also replacing sockets when required. Gardeners may accidentally cut underground cables.

I am guessing t8's are fairly new. Not really. They cost more because they aren't produced in as large a quantity as your basic cool white T12s. Also they (usually) work only with electronic ballasts, which are common in commercial settings but still somewhat rare in homes. To be clear, just replacing your T12 lamps with T8s won't work. YOu also need a cold weather electronic ballast for the fixture. Many of the E-ballasts not rated for cold weather operation DO work well in cold weather, but don't bet on it, get one that's meant for cold weather. My experience is that electronic ballasts rated to operate down to 0 deg F or lower don't cost much more than those that aren't, but that probably depends on where you buy them. I just remembered, one thing you can try without replacing fixture, ballast, or lamps, is getting those clear polycarbonate protective sleeves for the lamps. They keep a bit of the heat in, so the lamps warm up faster. No guarantees, but they might help.

My Regency woodstove came with a lifetime warranty so maybe the gas units do also. Time to contact the dealer.