It depends really. If it’s a daily to do list then I think you should limit it to the top 10 things you want to do today. Top 10 things don’t have to be the longest and hardest tasks, it can simply be ‘play bronnie on spotify’. It’s something that you want to make sure you do and by ticking it off you get a sense of fulfilment. You can have a yearly to do list with hundreds of things you need to do, which could lead to a ‘bucket list’ of cool things you’d like to do. I don’t believe a to do list should have a limit, it just depends when the deadline is, if you want a to do list for 1 day, then stick to 10 things, but if it’s for a week, it’s good to have it never ending filled with bits and bobs to conquer over the week.
Yes, do not overwhelm yourself with doing too much in one day. Even if you make a long to do list have at least 3 top priority tasks for the day. The things that must get done to help you feel most accomplished.