Securom doesn't matter to Macs. It's a PC program.
EA store will be somewhat necessary for Sims 3, as the second 'hood is there, etc.
I'm wondering, since you NEED to install EA's "download manager" to get their Sims 3 content, if this download manager will be Mac compatible. Sure, the actual *content* might be, but will we be able to get to it?
You cannot sell your own puppies in those display cases, as far as I can tell, I think you can only "stock" them using random animals.
The only way I can think of that you could sell your puppies is to set your home as a business, wait for the customer, and use the sales>pet.. option. Even then, I doubt the game would let you sell them as puppies; you'd likely have to grow them up first.
Though the "pet store" may be cute, it's not useful at all as a home business, IMO.