I want to start an online business selling my web design services and taking orders online. The prices will be fixed with 3 or 4 different packages to choose form.

Eg: $499, $799, $999 packages.

Can I use a generic, electronic 'Agree to Terms' type on contract prior to submitting order form?

I would be requesting a fifty percent deposit prior to starting work and the final fifty percent at the time of delivering the client approved design.