You can start a small projects with any amount, all you have to do is create an idea that gives you a trademark. Because all clients or investors are looking fresh and newly idea that excel in the crypto currency community. If you do that you don't need to have a capital for the projects, because the sponsors are willing to provide you all your needs for your project.
You cannot say any amount. It all depends on the kind of project and the budget it needs to start no matter how small the project may seem. One thing is confirmed, starting little is good and it can be built from there but whoever is going into any business will still have to be realistic to know what he actually needs to kick the ball rolling for that little start without flopping and building it from there.
I believe any small amount also will be enough when we are having a new innovative business idea as more people will be ready to contribute when the idea is good so they will help a business to get built.
He mentioned that he want to start the small project with the bitcoin investment. So ICO, trading and GPU mining are the best platform to start investing your money. Check about the investment option with the person who are knowledge in the concern investment option.
They could be able to help you to increase profit and how to go with the investment and make profit with the low budget.
For me the knowledge is the best thing because as you said it is best option to invest on the ICO and GPU but for this the most important thing is the experience so if you are having the experience and you want to make the money then it will be very easy for you. For me the trading is the best thing to invest but if you are not having the money o trade or to invest you should use the bitcoin investment and the signature campaign.