yes you can , you can learn from w3school the coding part and the designing part you can learn from tut+ site
It all depends on you. I think that you can answer this question by own. If you are strong enough in photoshop, css and HTML, why not just check your skills by designing something for your website?
You can create a site even after one month if you are being teched by someone who knows their business.
Yes, you can create your site with your knowledge but if you want it,s work better then other sites you should learn the advanced features of web designing. it's very helpful for you and it's all depends on your skills and confidence. Keep it up.