We will fire a couple big questions right back at you!
(1) Do you want customers to be able to check out directly on your site with no prior permission or assent on your part? If no, you probably do not need traditional e-commerce.
(2) Do you have custom or fixed pricing? If you have fixed pricing, then ecommerce may be a possibility. If you have custom pricing, you may just want to use a great invoicing software of b2b customer portal software.
See the above #4 B2B Ecommerce section.