Not sure if this is still needed - but I'm new here and want to say hello!
With regards to a cart - due to the security issues involved, i would recommend against making your own cart and instead use an established one - paypal have some pretty easy to set up systems i believe.
A slider, in and of itself - is very easy to make using HTML 5, but what do you want to connect it up to? If you let us know that they I can advise on how you should proceed.
Google the promo thing, millions of them out there