self employed autistic and looking for nice girlfriend

I think getting involved in social groups/clubs focused around things you're interested in (or think you might enjoy) is a good idea, that's how I met my (also autistic) other half when I was your age. We've been a couple for about 5 years now. 
Doing so will also generally help you with communication as you are interacting a lot socially but the focus is on the activity, so there's considerably less pressure and more room to observe and learn the social code.

As a woman, cold approach would totally freak me out; I think you're only likely to get the numbers of extremely self confident and socially outgoing women with that method. If that's what you're looking for that's fine, but it might not be a great fit if the situation is then that they are always wanting to take you to big group events that you fundamentally struggle with and therefore don't enjoy.
Meeting someone through an activity you already enjoy does mean you are more likely to get a good personality match and have at least one shared interest to build from. 

I am also bad at telling when people are interested in me. It took literal months of being apparently very obviously interested in eachother to those around us before me and my equally oblivious boyfriend finally admitted we were interested TO eachother (with the help of alcohol)! XD
 
I believe that some good signs are is if she is behaving in a very playful/childish manner with you different to the way she behaves with other people, focusing on you disproportionately in group situations, or generally being very keen on physical contact (not necessarily of an intimate nature, just contact in general). That's how I apparently come across, anyway! 

I think getting involved in social groups/clubs focused around things you're interested in (or think you might enjoy) is a good idea, that's how I met my (also autistic) other half when I was your age. We've been a couple for about 5 years now. 
Doing so will also generally help you with communication as you are interacting a lot socially but the focus is on the activity, so there's considerably less pressure and more room to observe and learn the social code.

As a woman, cold approach would totally freak me out; I think you're only likely to get the numbers of extremely self confident and socially outgoing women with that method. If that's what you're looking for that's fine, but it might not be a great fit if the situation is then that they are always wanting to take you to big group events that you fundamentally struggle with and therefore don't enjoy.
Meeting someone through an activity you already enjoy does mean you are more likely to get a good personality match and have at least one shared interest to build from. 

I am also bad at telling when people are interested in me. It took literal months of being apparently very obviously interested in eachother to those around us before me and my equally oblivious boyfriend finally admitted we were interested TO eachother (with the help of alcohol)! XD
 
I believe that some good signs are is if she is behaving in a very playful/childish manner with you different to the way she behaves with other people, focusing on you disproportionately in group situations, or generally being very keen on physical contact (not necessarily of an intimate nature, just contact in general). That's how I apparently come across, anyway!