If you want to use Odoo, why not have one Plone site and one Odoo and just a 'rewrite rule', so for example
shop.mydomain.com (odoo ) shows up for the user as my domain.com/shop ?
If you NEED to use Plone for the shop, I would drop Odoo completely, and use bda.plone.shop.
For the user, it will be flashy enough (other Plone e-commerce add ons are not) and do most of what you want.
(I am a bit uncertain about the discount part (with things like a coupon)
One thing to consider is probably: How big is this shop going to be ?