Hi there. Your pup is a cutey and his sits are pretty adorable. Looks like he's going to be very food motivated. You're doing a great job, and your clicker timing is really good. Just a couple of things to add to your training.
You probably already know when you are first teaching a command to get them to do the action first before adding the word. That ensures they are actually understanding the command rather than just offering behaviours.
I'm guessing the throwing food on the floor is because you have the camera in your hand. With the rewards though you need to do them while he is still sitting, otherwise you are rewarding him for getting up, not for sitting. The reward should be at the same time as clicking as well to reinforce the click.
Do you have a release word yet? The release word is like an 'at ease' so it allows him to stop sitting or dropping or whatever you are teaching. I use okay, or you can use release or free or something similar. It's very handy to have a release word when you are doing something like crossing the road. They know they have to stay in the sit until you give the release word.
With the 'leave it', there are 2 approaches. One is to give the treat you ask them to leave as a reward, and the other is that they never get the thing they are told to leave and get a different treat instead. The latter teaches them they must look to you when you tell them to 'leave it' rather than focusing on the thing they are leaving.
I switched from the former to the latter because we get a lot of snakes where we walk and I wanted my dogs to know that they never get the thing they are told to leave. Mind you, when Tully comes across a snake my 'leave it' is usually a half scream so it's hard to mistake my message, with Deska it's usually a growl because it's always food on the ground. If there is something they have to leave but will get (say access to another dog) I tell them to wait. You can teach them both by just having different words for each method. Sorry if I'm confusing things, just thought you might have big snake issues in rural Qld so teaching him the absolutely leave it command might come in handy.