Yes - that's perfectly fine. I started the same way.
Can I apply if my english isn't perfect?
Yes - Welcome to the club! A lot of my students and other established solo ad providers don't speak English fluently. No worries. 99.9% of all communication with your customers can be chat-based anyway (usually via Facebook or Email chat)
How much can I expect to make with this business model?
I'm not allowed to present these details on the WSO thread, so I recommend you to visit www.soloaduniversity.com. You will find the latest in depth-case studies there.