I think you’re partially on the right track here - taming any animal is just about hitting an exponentially larger overbalance of positive experiences in comparison to negative experiences in terms of your interactions with your bird. For example, it’s good that your not forcing him out of his cage as that would lead to a negative experience.
It’s great that you’ve found a treat that he’ll go for - treats make for great reinforcement. For the first little bit, I would try to get him to come take a treat from you rather than you getting him to step up. While it may not be the case, it sounds like you’re missing his queues that he doesn’t want to go near your hand (when he backs up) and essentially forcing him to submit to doing so. If I were in his place, I would label that a negative experience and actually see that as being detrimental to building trust.
Because a lot of birds are afraid of hands, when beginning to interact with a new bird I like to be mostly hands off. Training hands-off tricks is probably your best bet for now as you’ll learn to read your birds body language while eventually attaining a clear form of communication between a queue and a positive reinforcement. I’ve trained every bird I’ve ever owned how to spin around on their perch for a treat as it’s an easy trick and good distraction for your bird if they become frustrated or obsessed with something and you need to displace them.
Additionally, because they’re less grabby - wrists are quite a bit less scary then fingers. Once your bird gets comfortable coming to you and you want to train them to step up, start with getting them to step up on your wrists and over the course of various training sessions see if they become more at ease with stepping on the back of your hand, then eventually your finger. Also, because lovies are really small birds, I usually train them to hop up from their body’s length of distance away. This way, I’m not really invading their personal space and they can back away if they’re too afraid (and we’ll go for a spin trick to make sure the process still ends positively) but you can also avoid a bite if you’re ever working with a moderately agressive bird.
Sorry for the novel, good luck with your little guy!