You can do as many as you like. But, in general, I recommend you stick to 1 at a time and get it done!
In general, the Goals further up the (members-only version of the) list are more important to most parents than those further down. But you can do them in whatever order makes sense to you. You can also add your own Goals.
And you don't have to ever do all the Goals, it's up to you.