First time applying for fiancee visa. Any advice?

After nine months of dating my girlfriend and I have finally decided to get married. We didn’t have the very romantic proposal or anything. We just discussed the idea of marriage and one thing lead to another. Despite the informal setting, we’re still both serious of our plans.
This is why I’ll be working on her fiancee visa on her behalf. I don’t know if it’s possible for me to process the papers instead of her. I don’t know anything about this and neither does she. I had a friend who had a visa kit after joining the romance tour in China. I wonder how I could also get one of those kits.
Should we tap immigration experts to do work for us? How much does a fiance visa cost? What are the requirements needed. Advice please.