Firstly, if you are worried about playability, you should be using the Lite version of this modpack. This one is more for dev-testing compatibility than anything else.
Secondly, regarding your rocket question, you do not need a crusher to launch rockets from Nauvis. The vanilla Rocket Silo technology allows you to build the Rocket Silo, space platform starter pack, space platform foundation, and the ability to build rockets. Once you launch a rocket and build your first space platform, you will trigger the thruster tech and related fuel recipes, which allows you to fly to Muluna. There are no harmful asteroids on the route from Nauvis to Muluna, so you won't need turrets, asteroid collectors, or crushers (since you won't be needing to craft any ammo yet)
Perhaps there's some of misunderstanding on your part, but the Crusher is not an essential piece for a Space Platform
If you were wondering about how to craft the fuel, you don't need to rely on asteroids for that, when you are orbiting Nauvis, you can just send up the ingredients you need for your first space flight, and use chemical plants to craft the fuel. Even just a tiny amount of fuel is enough to get the ship moving, which will eventually get you to Muluna, where you will gain access to the Crusher, and more efficient space travel recipes.
If you are wondering why it is set up this way, you will have to ask the Muluna dev about that; they are the ones who modified the tech progression, and it's only included in this pack for ease of compatibility testing. Due to these sweeping early space-age changes, Muluna is not included with the Lite version of this modpack by default (neither is Lignumis, for very similar reasons)
