I make my own curriculum and most of my teaching resources just as you are. The one thing to remember is once you have done them they are good for many years. One thing is to limit how elaborate you get with the themes and then add to them each year so it means making fewer items for each theme. Also remember that children love repetition so again you can get away with less the first year and then the second year add new items.

Even with most prepackaged curricululms you still need to do prep work. The difference is the ideas are all there but there are so many sites on the internet for printing directly from for free that it works well too.