Thank you for you comments...deciding is the hardest part, so many options! I'm going to go for mixed whites, mixed patterns, and just sort it all out once I've done all the crocheting. This way, if they stop producing the whites I'm starting with (though unlikely) I can use other brands/shades, and if I discover a great pattern in a few months time I can easily incorporate it.
I've had some fun today brushing up on my crochet...I realised I hadn't actually done very many granny squares before, and I found purlbee's wonderfully clear tutorial very helpful. It was also easier to start with string and a very big crochet hook, so I could understand the details better. I havn't yet attempted the garden square...I need to decipher some of the terminology first.