Your method is pretty much right. Its not an exact science and I would aim not to over do the beans and you should get a very decent roast.
Is that the roasting position of your gun? I usually have the tip a couple of cms above the top of the pan. This is the way I was doing it for ages prior to getting my data logger, which just makes it easier to see how your roast is progressing and when you will get second crack, but is not essential:
I keep the gun a couple of cms above the pan pointing vertically down near one of the corners on full heat/fan until first crack (~10-15 mins), then raise the gun another 2 to 3 cm and keep it there until I hear second crack (another ~5-10 mins), then dump and cool beans as quickly as possible. Your cooling sieve doesnt look very "holey" to allow cooling air through (presuming you are using a bucket/fan setup for cooling).
My first BM looks to be same size as yours, and I used to do around 500 grams green. Smaller batches will probably roast more quickly.
I have been experimenting on extending slightly into second crack based on what I have read here, but I find I need to be quick to make sure the beans do not get over done.
Give it a go and I am sure you will get a great tasting roast.
Its also interesting to try the beans everyday and taste the difference as they develop everyday.