The game is under development, which means that we are still doing quests and in each new version you will receive new content. If you've played 0.4 but want to skip content from 0.4 and go straight to 0.8 content, we've added a "New Game+" section where you can skip quests. This is very handy to keep track of new content in the game.
About the characters. The same characters will play in the main game, only their skin will change.
You cannot use saves from older versions, but you can skip quests that were completed in previous versions. For example: In version 0.7 there were 14 quests in total. In version 0.8 you can skip all 14 quests and go straight to the new quests. To do this, use the section "New game +"