Yes it's a lot to take when you first start skinning the UI but soon enough you will get hang of it, trust me
You can start be finding
ID="toolbar" tag. This PanelFile element controls the mainbar. If you remove that whole PanelFile section from the skindefinition.xml the skin will start using the default values and therefore moves the mainbar as it is in the stock UI. Then you just have to reskin it.
ID="toolbar" was later renamed
ID="ID_UISkin_Toolbar". You can find the updated Panelfile/Element ID's from SkinDictionary.txt from the latest
Art Asset Pack.
ArtAssetID="LetterBoxBottom" assigns the mainbar graphical output (actual skin file). This was later renamed
ArtAssetID="letterbox_bottom".
Hopefully this gives you some tips to how to proceed (I wouldn't wanna spoil it all for you now wouldn't I hehe). If you need further assistance just ask and I or someone else on this site will try to help.