You can do a lot with 100k investment. I started my e-commerce business right after 9/11, right after I got laid off. I started with 25k. 20k for products and 5k for advertising. My first nine months, I generated 600k in sales and my second year I generated 1.2 million in sales. The high sales volume, thanks to the right products/brand that people were looking for at the time. Manufacturer did a lot of advertising and educating the public. So, when I advertise on Google, people will search for specific product / brand. At the time only 3 companies selling that particular brand.
With increasing competition and discounted price, I spent a lot of money on online advertising to build my customer base, and had to consistently advertise and provide top notch customer service. I was shipping out of my 3 car garage, and ran the business from my home office. Just myself and my husband, with me doing 80% off the work, from processing orders, web maintenance, inventory control, vendor relations, product research, etc. I am a hands on entrepreneur and learned from mistakes along the way.
Bottom line, to be successful in an e-commerce retail business, you must choose the right product(s) to sell. Retailer of many different brands or retailer of your own brand/product or a service business. You must have your niche. You must dfferentiate yourself from competitors. You must reinvest on new products, you must understand loss leaders, bulk buying, MAP pricing, private label, etc.
Remember to allocate $$ for internet advertising, PPC, SEO, Viral, Social Media, Be creative and make your advertising $$ stretch. Stick to your budget. Lots of hard work, but it will pay off.
Once you have a good business model, you can take it up a notch with franchising. Good luck.