i don't think you can combine tours as you said, each will take roughly a day.
the penguin island direct is a half day tour so you can choose to do shopping in the day/afternoon and head off to see the penguins at night

ermmm not very sure about strawberry picking but yeah, prob not the good season to be heading down to do that. give Half-tix a call or check out other websites

i'll try to get the Yarra information up for you tonight.
highlights?? what are you looking for? most of the guys here have suggested quite abit and there's so much to do for a week's trip excluding shopping and others