Some of your above requests are easier to achieve if you download the latest beta. There's an "Options" button in the toolbars file that you can enable which acts as a compact menu when you right-click it(most of the buttons have right-click menus). That'll allow you to hide the menu completely. It also comes with the more minimalist IE Based Klassic theme which may be more to your liking. Just switch to that theme in preferences.
http://kmeleonbrowser.org/forum/read.php?f=1&i=19584&t=19584
* is there a way to hide the title bar (with the title and minimise, maximise and close buttons) while still keeping the task bar visible?
Yes & No. Not while keeping the taskbar visible.
* when making a theme, is it possible to make the scrollbar a certain color? or can this be done seperate of the theme?
You'd have to get into modifying the chrome I believe. It also wouldn't be specific to the theme...the scrollbars would always look a certain way if you modify the browser. So short answer is not easily. There is a way but I've never tried to. Someone may post how to.