I have a similar question as apptiger to the rebuildable experts since I am using Carto Tanks.
Noted in the funeral picture by SeniorBoy that his device was on a Provari.
If I went for the Kayfun Lite what Voltage and Batteries are you using for the Provari. I am also assuming the Kayfun has a 510 connector and no adapters are needed.
Believe also that someone posted previously this was a good place to purchase;
Kayfun Lite plus - InTaste
As far as batteries go, use whatever size you want. I guess it would depend on how much you vape and how often you like changing batteries. I have a full size Provari and use a 18650 battery mainly because in my accident last month I lost my 18490 cap. Using the 18650 I only switch batteries every two days but I'm not vaping as much during my time off as I normally would.
Voltage would depend on what resistance of coil you are building. Here's the link to the chart I've always used to determine what voltage I use. This is from PBusardo's website TasteYourJuice.com
http://25.media.tumblr.com/tumblr_m9dkanCt0I1qc8949o2_1280.png
The Kayfun and Russian both have a 510 connection so no adapter needed for the Provari. You can buy the beauty ring as well to make it have a flush look on your Provari. One day I may get one but the look right now doesn't bother me.
Akdare turned me on to Intaste. I ordered my KFL+ v2 from them on Sunday of last week, it was shipped on Monday and in my hands two days later last Wednesday. Germany to Ohio in 3 days.
Regarding Kanthal wire size: depends on what resistance you're looking for. The Provari v2 & v2.5 will fire down to 0.8ohms. I've got a Russian running at 1.16ohms and a KFL+ at 1.25ohms right now. The thicker the wire the lower the resistance. Thicker wire takes a little longer to heat up (we're talking by one, maybe two seconds or so) and lower resistance will take more energy from your battery. Remember when looking at wire gauge that the bigger the number the smaller the wire, so 30G will be smaller than 28G.
When I wrap a coil I like to stay around the 1.2ohm range. I use a 1/16" drill bit and 28G Kanthal. Eight wraps usually gets me approximately 1.15ohms and nine wraps 1.26ohms. I believe the most popular wire sizes are 30G and 28G.
You'll need some tools for a rebuildable though but not many. My KFL+ v2 from Intaste came with a micro screwdriver (Philips/flat head combo). I also use a slightly larger Philips head for the bottom screw because I like to use the bottom fill port. A drill bit as a form for the coil. A small pair of wire cutters. Either a propane/butane torch or even a lighter to anneal the Kanthal. An ohm meter box to test the resistance of your coil (I believe Intaste has these as well but they can be hard to find just because they're always out of stock). Here's one from Mt. Baker Vapor to give you an idea of what to look for:
Ohm Reader - Mt Baker Vapor - Electronic Cigarettes
Here's a picture of my little build kit:

I already had all of this from when I built my last computer.
You'll also need some wick. Most people using micro coils go with cotton. I believe Jerms prefers sterile rolled cotton from CVS.
http://www.cvs.com/shop/product-detail/CVS-Rolled-Cotton?skuId=95549
I use organic cotton balls from Walgreens.
http://www.walgreens.com/store/c/studio-35-beauty-organic-cotton-balls/ID=prod6097939-product
It costs roughly $3-$4 for a lifetime supply. I get around 16 wicks from one cotton ball. When using a cotton wick less is more. Make sure the wick slides through the coil fairly easily as it will swell when you put juice on it. Also never dry burn cotton because it will burn up. Once you get the hang of it changing a wick takes a couple minutes. The micro coil can last months and the wick for several tanks full of juice.
Here's some pics and video from my favorite reviewer on making a micro coil:
Taste Your Juice | SO I WAS PLAYING WITH MY COIL TONIGHT (MICRO-COILING THE RUSSIAN)…
Taste Your Juice | THE KAYFUN LITE AND THE RUSSIAN 91%
It may seem daunting at first but once you get the hang of it it's really quite satisfying. Vaping some great juice from a wick and coil you made yourself. A coil will last a month or two and the wick depends on your flavor preference. Building a wick and coil from scratch now takes me 10-12 minutes and I'm on the slow side.
Hope some of this helps.