I use the cores/mouthpieces from e-cig.com ONLY with my ecigs I bought from them e-cig.com or bestecig.com
The penstyle/801 inhaler/mouthpiece from e-cig.com does fit the penstyle/801 I bought from puresmoker BUT IT'S LOOSE. The ecig kept dropping while the cart was still in my mouth. My ecig is more important to me then the carts.
(Hope what I wrote isnt too confusing)
I also had problems with carts not being interchangeable & got confused when thought all pens were the same but they're not..
Best e-cig sells DSE 801 (probably ecig.com too ), so best ecig &ecig carts are interchangeable while Puresmoker sells RN4072 pens
DSE801 atomizers are shorter and slightly wider at bottom - so their carts are in turn shorter/wider also they don't click/snap into the atomizer
RN4072 - longer and skinnier..carts too and snap into atomizers
so if you use DSE801 cart on RN4072(puresmoker) they are loose as don't snap in as RN4072 carts and are shorter so may not wick as well since filler is further away from the atomizer .
If you use RN4072 cart (puresmokers) on a DSE801 (best e-cig )- since the carts are slightly longer , they will stick out a bit although some people say no fluid leaks , I find that the cart end can melt onto the atomizer a bit and cause burnt plastic taste..
I've kept the carts separate for now although I've tried to snip off a bit of plastic on the RN4072 carts to shorten and works fine..
Hope this helps - although this really can get confusing..

I can't help with the other paarts of your post..mini cart etc..hope someone else can!