Yep, I use these, and they work just fine. Just be careful when you're sliding the cartos into and out of the tank. Either end-cap could pop off, causing your juice to spill out (bottom o-ring), or flood your carto when you pop it back on (the top o-ring).
Like Baditude and many others, I suggest a tank-refilling tool. It fits into your cartomizer like any drip tip. It makes refilling much easier and protects your o-rings from wear and tear (cartomizers are metal and WILL damage o-rings over time).
If you want cheap to practice, I'd say go for a Smoktech DCT tank. DCT stands for Dual Coil Tank, but you don't have to use dual-coil cartomizers in them. In fact, I suggest single-coil cartomizers, but that's my personal taste.
Here is a link to what I use:
Tanks:
6 mL:
VC-DC 'Colors' Tank w/ DC LR XL Cartomizer & Drip Tip (510, 6ml) - VaporCast
3 mL:
3ml VCDC Tank - VaporCast
Replacement Cartomizers (flanged, factory-punched with
2 holes):
2.0 ohm Dual Coil VC-DC Tank Replacement Cartomizer Double Hole (510/DC/LR/XL) - VaporCast
To answer your question, yes, these two holes should work fine with your 50/50 juice. Remember, if you use a carto punch tool to make a new hole or an existing hole bigger, you could very well deform the cartomizer and make it almost impossible to remove and/or push back into the tank... Be very careful and practice with dead cartomizers if you eventually want to go that route.
EDIT: Priming a carto can take up to forty drops, going N E S W into the polyfill, while rotating the carto, avoiding the center hole. Anything less I found can cause instant carto death and that nasty burning electronic taste.