I don't use the Provari myself, but they have a very active area (the Provape ECF Suppler area).
I don't know of any added/different pluses or minuses of using the unit with the extender cap vs. not, though expect it is a shrug, that literally the extender is just a screw-on extension so shouldn't affect device safety/performance in any way (other than longer run time from a larger battery).
Provape sells good gear, and the AW IMR batteries are well known good items (though many counterfeits -- Provape will have real ones). The other very good IMR that I've been hearing about are the Panasonics, though I don't know if they're available in the size you want. SuperT Manufacturing and RTD are two other very well known vendors of good chargers and IMR batteries.
Personally I use the XTAR WP2 II charger, which has very good reviews and costs about 1/2 as much as the very popular Pila chargers. It has both 500 mA and 1000 mA max charge rates, via a switch. Use the 1000 setting if your battery is >= 1000 mAh, stay with 500 for smaller batteries. The Pila charger is the other top end charger -- I really don't know if it's any better than the XTAR, which I bought after reading recent reviews on some of the light forums.
(Technically, the XTAR has a very nice charge characteristic, extremely low post-fill trickle, and a very low discharge rate once power is disconnected. A "cool factor" thing, for me, is it comes with a 12VDC car adapter, if you're ever stuck in the middle of nowhere, need to recharge from your car.)
With the XTAR an 18490 would work fine with the included base set of spacers. For shorter batteries (I also use some xx340 batteries), a second pair of spacers is needed, they cost about $1 for a pair. I'm not sure about the Pila and spacers.
If Provape sells either the XTAR or the Pila, no problem. If not, while whatever they do carry is good gear, you might want to go for a Pila or XTAR from elsewhere.
This is the little timer I use:
http://www.amazon.com/Belkin-Conserve-Socket-F7C009q-Energy-Saving/dp/B003P2UMS0
Switch on the side lets you select one of three durations. You need to test your batteries with your charger, to see how long they take for one full charge cycle. My smaller batteries all charge in under 3 hours on my charger, so I use 3 normally. Set the duration, then leave it alone, just tap the button on top to start a cycle. It can handle up to 1500W, no problem with our tiny draw chargers, and draws no power itself when off.