I have had nothing but problems with my Kanger 25mm Subtank. Lots of leaking and burned 0.5 coils. I have purchased the #14 and #30 o-rings and the #30 o-ring worked the best. After 5 phone calls I finally got somebody at Kanger to send me the updated Kanger Subtank o-ring kit. That kit has helped but it still seaps liquid . Everybody I know with the mini's and nano's have no leaking issues and like them alot. I got the big Subtank before the mini and nano's came out and wish I hadn't spent $45 on it. I forgot to mention this is my second 25mm subtank because my first I had to exchange after a day due to massive leaking. Any mech mod will push any of the subtanks fine or any 30watt device that can go down to 0.5 ohm. I would want suggest at least 30watts on a subtank. You don't have to go that high but you will want to be close. You can pickup a mech mod and 18650 batteries and a charger for pretty cheap these days.
Just in the interest of balance, I too have the 25mm Subtank and have had nothing but trouble-free vaping from it - both using the 0.5 and 1.2ohm prebuilt coils and the RDA section. Zero leaking (except for a little condensation around the air flow holes) and no weeping at all.
I thought I would never go back to clearomizer vaping until I got this subtank - it's really good.
OP
As for the difference between the mini and the nano, the main difference is you can try your hand at rebuilding with the Mini as it comes with an RDA deck. Of course there are the differences in size and capacity too...
Pretty much any 'battery' (assuming you mean APV or Mod) will work for the subtank with the 1.2ohm heads, if you want to use the 0.5ohm coils then you will need to make sure the device you are buying can fire down that low. I would also recommend you pick one that can deliver at least 30 watts.
If you are asking about a battery to put in a mechanical, you need to use an IMR or IMR hybrid battery like a Sony VTC4, a Samsung 25R or an AW 18650 20 amp (among others) would all be perfectly adequate to run a mechanical down to a 0.5ohm resistance.