COATING YOUR SD:
And also try this excellent tutorial by Marta/astrosnik

and also this great tutorial by Aisha.

Since the dolls have only been around for a few years, people are not quite sure how they "age". Some people have said that the dolls may get paler with time. Others say that the doll may "yellow". Volks does say though that you shouldn't leave your doll out in the sun too much (or leave them in a hot or sunny place in your house). Volks said that unless you leave the doll in direct sunlight over a long period of time, the doll should be fine.

Dollfies are made in a factory, and while their quality is very high, often there are a few rough edges or seam lines on the dolls (not always). If this is the case, Volks encourages you to carefully sand your doll. But if you do, the finish that the doll comes with obviously will be sanded off.

Point being if you sand your doll you might want to coat it. A lot of people choose to coat their doll anyway, regardless of whether they sand their doll or not. This helps protect the doll from stains and from sunlight. Obviously the safest thing to do would be to sand and coat your dollfie, however if you are careful with your doll it may not be nessesary.

The unfortunate thing though is that coating gradually takes wear, and eventually you may need to coat your doll again as the coating becomes scratched off.

THINGS YOU MAY NEED TO CUSTOMIZE YOUR DOLLFIE:
1) Water proof sandpaper sponge
2) Sandpaper (various gauges, start big and work to super fine)
3) Hobby knife (to remove putty from eyes)
4) Mr.Super Clear (coating spray for after you are done)
5) String puller (you can find it at dolls supply shop or you can make one)
6) Putty (for the dolls eyes) (you can also use WAX from Tallina's to set eyes, or even a kneaded eraser!)
7) Paint thinner (Mr.Color thinner is recommended to remove eyes, paint, etc.) You also may need this to dilute your paint. Be careful when removing paint so that you don't DAMAGE the skin of your doll. You can also use non-acetone fingernail polish for removing paint.
8) Liquitex acrilic paint colors OR Mr. Color (by Gunze Sangyo) to paint your doll. You can also use oil-free artist chalks and non-oily human makeup to do your doll's face-paint. Seal with Mr. Super Clear Matte after you are done.
9) Liquid Rubber (optional, but its good to put on the head so the wig wont slip) You can also use velcro for this.

SANDING: make sure you use wet sanding sponges to do it. Makes it MUCH easier. start with medium grade and worked to super fine.

Lots of links on taking apart your doll as well as doing makeup, etc...
A japanese site showing how to sand, coat and repaint your doll (japanese)
Taking apart your Dollfie (japanese)
Sanding the Seams of your Dollfie (japanese)
Coating your Dollfie (japanese)