Just finished two rebuilds, having never rebuilt any atomizer before. It was quite easy and fun! I used 32 gauge kanthal A-1 and 2mm silica. Wrapped it 5 times for a resistance of around 2 ohms. The coils lit up evenly right away, so I guess no hotspots!
The second head vapes better, no surprises there. In the first I wrapped 2 wicks, but it turned out too thick for my 100% VG. The wicks are thicker than those that are in the T3 by default, maybe they sent me 3mm by mistake.
If I learned one thing (besides, you know, making a coil), it's that one should always be careful with one's grommets. Two of the plastic "hat" grommets bounced away during the builds, but luckily I found them.
I am a happy vaper now, and I really recommend all T3 owners try this out. If you make a mess of it or don't find it fun, you can always order cheap replacement heads.