I too have a large classical collection.

A) a catalogue number ie the number i have already put on the CD case so that i can find it. EG. When i turn to album view of title I can see this catalogue number, or, in Record properties box
On the "library" tab there is a "reference #" that is automatically generated by OCD based on when you entered the recording. By clicking the arrow directly to the right of this number you can enter a custom number. Alternatively, to the right of this entry on the same tab is an entry for "location". You could enter your catalogue number here as well. Both can be displayed in the "Album Page" view. You can customize the "Album Page" by right clicking on the page and selecting, well, "Customize View".

B) i would like the composer to be surname first, then Christian name. Can this be done?
You can enter the composer's name any way you like, but you must click the arrow to the right of the entry to determine how the name will be filed. How you enter the name is the way it will appear on your album views. How you file the name is how OCD will locate the composer and order your tables if you choose to order them, as I do, by composer. I prefer to see the composer's name normally in album view but, of course, I file it with surname first. In table view you are able to choose which catagories you want to see and "Composer" and "Composer (sort name)" are two different catagories. Thus, you could have the composer's name show normally in Album view, which I prefer, but when viewing or printing out your collection from table view by choosing "Composer (sort name)" you will see the name as the entry you made for filing purposes.

c) Can i get rid of a lot of tabs i don't want...such as Credits, Recording, Notes.
As was said above, I do not believe this can be done. But I use the "Credits" tab regularly. Although entry of the credits can be tedious (especially for large choral works), it is here that you are able to catalogue conductors, orchestras, ensembles and soloists as such. As well, the "Notes" tab can be useful as well for containing any information for the album for which there is no appropriate catagory but you wish to see in the Album View.

As for entry of information, by far the easiest way is simply to place the recording in your CD drive and click on the icon for "Scan CD ROM Drive". If you're lucky the information for your recording will be available, but be advised that if the recording is rare or brand new nothing will turn up and you will need to enter everything yourself. As well, the track information is often in a format that I do not like and I wind up re-entering myself. This is especially important for classical music as very often an album will contain several different works and the only way to know where a particular work is located, at least that I have found so far, is in the tracks view. You can also, as I did, create a custom tab that lists all the works contained on the album by composer, title and opus or catalogue number.

I know OCD is rather daunting at first, but once you find a routine that satisfies you, it's very simple to use. Good luck.