There are a plethora of better tools than photoshop for this kind of work, that will make your life a truckload easier.

e.g. NukeX has a free trial (http://www.thefoundry.co.uk/products/nuke-product-family/nukex/trial/) or a Personal Edition which is free, and lets you learn the product.

Grab some paint tutorials and give it a go.

or jump to the Paint and Roto section here:

Grab the PLE version below whilst learning, then you can use the 15 day trial once you are up to speed :)