There are no spas or hot tubs in Sims 3 yet
Yes you can now! You have to have the sims3, by itself, you WILL have to buy the sims3 pets, which you can get from gaming sites, the best one is The Sims3.com. :)
No
buy birthday cake
You can buy the CD from a shop or you can buy from the internet and download .
You would have to buy sims 3 World Adventures.
Walmart, Bestbuy, or the Sims 3 website.
buy exercise equitment
Of course. Just like Sims and Sims2.
You buy the game, install it and then you play it.
Buy a stroller to push.
Firstly your Sim must go to Town Map > Spa > Become Partner. Then, if you wish they can buy out the Spa by going to Town Map > Spa > Take Over Business. This will allow them to own the spa. They can collect their profits once a week from the spa, and, if you wish, rename the Spa.
There are many sites that one can buy spa accessories from, such as SpaShopper, and CalderaSpas. Google has a large listing of sites that sell various spa accessories.