You might want to check your blowoff tube isn't pinched or clogged if your lid is bulging like that. It is a sign you have (or had) way more pressure than you should, and could be a big mess waiting to happen.
Bulging lid, lack of bubbles, etc, isn't a reliable indicator that fermentation is done - the only way to know for sure is with gravity readings, taken a couple days apart. If they are the same, fermentation is complete, if not, give it a couple more days and sample again.
For taking the sample, when I used a bucket, it was as simple as sanitizing my hand and a cylinder and carefully dipping it in (trying to keep my fingers out as much as possible). You can also use a sanitized turkey baster to pull enough liquid for a sample, or pick up a Wine Thief, they work fairly well but with buckets you may not get enough depending how wide the bucket is (not enough depth for a big sample).
As for final gravity, you should have taken a starting gravity (original gravity). Multiply this by the average attenuation for your yeast and you'll get an approximate final gravity. If you don't know it, post the kit name and maybe someone has some old notes that can give you an idea. Based on the color and a wild guess, I'd say you should finish 1.008 to 1.012, but the yeast is done when it tells you it is done
EDIT: The link you posted says expect a FG to 1.011