Hi Elaine, good for you, it looks like a great lens and I'm sure you'll have great fun with it. You realise that you can get it for £450-£550 if you shop around?
The Canon collar costs serious money. If it were me I'd try the lens hand-held for a while to see if I could do without the collar. I have the Canon 300mm f\4 and it almost never goes on a tripod but I don't do landscape photos.
If you really want the collar have you thought about trying a cheaper one? I realise that some of them scratch the lens body but some apparently don't. At least the reviews for this one say not -
JJC TR-1 tripod mount ring replaces Canon Tripod Mount: Amazon.co.uk: Electronics - if it were me I'd order it, give it a try and send it back if not satisfied. I use mostly Canon stuff but some of it really is vastly over-priced and 3rd-party stuff can work just as well.
Good luck!