Customizing default DarkChocolate theme

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Hi, im new to C5 but really love it and i hope it will improve some things in the near future.

For starters, i have several questions that i'd like to be answered here if possible.

1. I'm trying to add global top navigation menu bar which will consist of images having to states, ie. colored when mouse hovered. Also, that hover version should be displayed when the button is active (ie. on the buttons's target url).
Is is possible to designate such things to image urls? I think i may have seen the option to select another state image.

If all of this cannot be (easily) done, i will have to PHP hardcode everything in the header.php element? If so, how should i go about checking the location (for example, how do i check if the user is on my Products page) so i can load active button image in my nav menu?

Another thing i'm noticing is that when i removed textual logo from the top section and also removed default menu, and inserted my custom Navigation block/stack, it just shows and overflows the main content section, which hadnt moved a pixel down. Why is this happening? Wouldnt one expect the lower content to go down when the top content becomes larger?

Thank you for your replies!