I like it, we have a guy at work from Scotland and he spells it Alister (maybe its a different name, but your spelling seems the way his name is pronounced).
I think its different enough, but still a real name. As far as nicknames, you can nn your child anything you want, my name is Amber and my family calls me Abbie - which is usually used for Abigail. We have Mary on our short list, but if baby is a girl she will go by Maggie. GL