Well my buddy who makes some great fruit beers with his Mr Beer, just adds it at the start. Though if you can lay your hands on a 3 gallon water jug, I would rack it after two weeks to the water bottle and add the fruit in secondary.
As to the yeast...you don't need to buy two tube for a small batch like that, heck you don't even need to buy a liqid...If you think the dry that came with it is bad (though it's prolly really fresh actually, they have a huge turnover) use a neutral dry ale yeast like Safale Us 05.
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