I started out with the same set. Fortunately, my flattening stone was ok. I did wind up buying a DMT C down the road anyway, and a few more. It's a great set.
Strops: A lot of guys cut their first strop. You may want to practice on an old belt, or something cheap at first. The modular paddle is a great tool, but I prefer a hanging strop for daily use.
For pastes and sprays, the modular paddle is the way to go. You can also check out Tandy leather, if there's one by you. They have leather for making belts that's great for strops, hanging and paddles. Check this link:
https://www.tandyleatherfactory.com/.../4523-190.aspx
Now, if there's a store by you, they normally let you go through their scrap bin. You always finds long strips of leather that's perfect for making paddles or hanging strops, if your so inclined. It's cheap, so if you cut it, no biggie, you have more...Also, I've found the staff at those stores extremely helpful, tell them what your doing, and they're usually glad to help....YMMV.
Once you get proficient at it, then buy yourself a nice strop...
Good luck....