Built-in bookshelves…

My project:  built in bookshelves for the office/library.

The space:  We have a recessed area on the far wall of the office/library that is 9’4″ wide, 8’6″ high to the start of the cove ceiling and 2.5′ deep. 

My thoughts:  I want to use some stock base cabinets from the Home Despot for the base of the built-ins.  Probably 2 of the kitchen sink wide ones as well as one set that is all drawers.  We need closed storage as S is kind of messy and hiding it keeps me from going nuts.  The base needs to be sturdy as it will be holding our 10 gallon fish tank and perhaps a slightly bigger fish tank in the future.  A couple of sheets of plywood and a sheet of cement board to form a counter which S wants to tile something “funky”.  I have agreed to this even though I am the least “funky” person in America.

Now, the shelves.  I really want them to have that built-in look.  So, should I build a book case that is 9′ x 5′ and just attach it to the top of the counter and walls?  That seems right, but I don’t know.  I’ve never done this before and I am no carpenter.

Help?