When I was using dating sites, I did the same on OkCupid, and signed up a fake account with the photos of a woman that was slightly above average in appearance. I was curious to see how many messages I would receive, but more importantly, the type and quality of those messages. I thought that would give me a better idea of how to write my own messages (e.g. if 90% of messages were asking the same question, I didn't want to also be asking that same boring question).
The first day I was surprised at the amount of messages I received. I think it was at least 10 in a few hours. However, it quickly faded, and after a few days, I was lucky to receive one message a day. That gave me a little confidence, knowing after the first day, the average woman was not receiving hundreds of daily messages.
Similar to what you said, a few people would get angry if I didn't reply. A third of the messages hinted at sex, thinking they were being clever with winky emojis.
In the end, on my real profile, I think I was decent with messaging. I sent out 200 messages on OkCupid (I focused on roughly the top 10% of profiles over a large radius), and had over 50% of those turn into conversations. My first messages were always similar. I would write one or two sentences that joked about something in their profile and asked a simple question. The idea was it needed to show I read their profile, it needed to make an attempt at being funny, and most importantly, it needed to be easy to reply to within a few seconds. When you write long messages with complicated questions, people don't want to invest the time in a reply, so they'll respond "tomorrow", which never happens. The other thing I did was almost always message women that were online at that moment, and I tried to turn the messages into a real-time conversation with instant replies.
As a simple example, let's say a woman's profile said she liked the Fast & Furious movies. I would write a first message saying, "If you had to choose between me and Vin Diesel, who would you rather date?". There's a high chance she would respond saying the obvious, "Vin Diesel :P", and then I would reply, "Would it change your mind if I said I had 100% more hair than Vin Diesel, and I go for ice cream on first dates?". These type of messages are very easy to reply to, innocent, and people can be creative and fun with their responses. In that example, I'm even hinting at a date, and it doesn't seem pushy. In this case I would then keep writing playful messages and then ask her to meet up for the ice cream like I originally suggested.
1. It implies you're so desperately single that even your friends are trying to set you up with people.
2. Whether true or not, it sounds like your "friend" is actually you, which comes across as very cheesy.