1. I can't find the Imperial City Waterfront District anywhere in the cell list.

2. When I save, exit out of the editor, then go back in and load my mod, then try to save. It says it is in use and I cannot overwrite it. This is keeping me from finishing my house

3. Can't find any tables (Not containers) just plain ones. Where are they?

1. Waterfront is in the Tamriel worldspace (part of the main worldspace).

2. Did you set you plugin as active file before you loaded it? You need to do that.

3. Not sure what you mean. Tables are under statics. Most of them start with the category, like LowerTable01 etc. If you can't find something you can use the 'find text' function of the CS to look it up. If you search for 'table' it will show you all objects that have the word 'table' in their editor ID.

Thanks, you answered most of my questions. The problem is that it says I cannot overwrite the Master file. However, don't I need to have that loaded as well as the plugin file?

You can never overwrite a master file. And you shouldn't, even if you could. Your esp is an extension of the Oblivion.esm. You can do everything you want in there to the Oblivion.esm so there is no need to overwrite the esm itself and cause a huge mess and compatibility problems with about every mod out there. It works like this:

1. When you start making your mod check the Oblivion.esm and load it. Do what you want to do and save. Now you can enter a name for your plugin and it will show up as an esp in your data folder.

2. Next time you want to modify the same mod you need to check the esp you created and set it as 'active file'. You don't need to do anything else. After you've done that you can load the esp and you will notice that the Oblivion.esm will load as well since it's the master of the esp. When you save after another session the CS will simply overwrite your esp with the changes you made.

My search function isn't working.

As Phitt said, you should use the "find text" function: Edit->Find Text. Of course it will not find any table objects, if the data from Oblivion.esm is not loaded into the Construction Set.

Tables are in Object Window, in WorldObjects-Static: LowerClasstable etc.