Your first question regarding cleaning: I have a cartomizer cleaning kit I got from Smoktek. Here's the link: http://www.smoktek.com/CartomizerAtomizer-Cleaning-Kit--With-10ml-Control-Syringe-Luer-lock-compatible-wcleaning-tubes-and-instructions_p_107.html
It works great. I use Everclear and distilled water to clean my cartomizers. The only ones I really clean though are the ones that I fill with juice, find I don't like the taste of the juice, and want to reuse them for another juice flavor. The majority of the time I use cartos I have previously filled with my favorite juices. When not using them, I put them in travel size q-tip holders I found at the drugstore. I can fit 4 to 5 cartos per case. Here's a link for one I use: http://www.minimus.biz/Q-Tips-Cotton-Swabs-Purse-Pack-J01-0556701-8300.aspx They will keep your filled cartos clean and ready to pop on your battery. I rarely clean the majority of my cartos, since they only last me a week or two anyway before I have to pitch it and use a new one.
I clean my batteries once a week by running a Q-Tip around the top and inside of the battery connection (I use 1300 Spinner batteries and a ProVari, and I clean them both the same).
Question 2: 100% PG (Propylene Glycol- a sugar alcohol) juice is very thin compared to 100% Vg (Vegetable Glycerine) juice. I find my cartos don't last as long with 100% VG juice, so I usually use a 50/50 blend of PG and VG. I don't think that using 100% VG will hurt your equipment, but you will burn through cartos faster.
Hope this helps!