The homeschooling education should include a strong textbook foundation as well as a thorough instructor and lesson plan. The home school education should not be exclusively based on education of the instructor or limited to a curriculum purchased.
Just because your child will be playing fun online games doesn't mean the same value won't be there. Create a comfortable study zone. Turn off outside distractions such as cell phones, radios or TVs.
Physical activity is not only important for your child's health - it will help them cope with the sheer physicality of interacting with twenty children on the playground. Bumps and shoves are inevitable, so make sure your child has lots of physical play to develop gross motor skills too.
Since 3rd grade math relies on the concepts that were learned during kindergarten, first and second grades, don't be afraid to start your child at a lower level.