(using 4.9.1 ) Overall desktop theme settings are still scattered, I hope that this is fixed in a couple of upcoming releases.
To change the desktop them (which controls the taskbar) go to
System Settings ->
Workspace Appearance ->
Desktop Theme. You probably want Aya, though you can download others (you may need to), there's also a details tab which allows you to customize more specifics.
To change the taskbar size click its
cashew and unlock widgets if they are not. you should see a height adjustment option, resize as desired.
To get even closer to windows you'll want to change your cursor theme to KDE Classic, and your Window Decorations to Redmond. Aya is not the best theme for looking like windows, I checked out the
Get New Themes and found one called "win-classic" it appears to look ok for the most part, I think a texture is missing for the selected window in the task bar. That theme may need updating before it is usable. You may find other themes that are a good fit.