I think you are going to get a similar response from most fitness professionals.
Rather than repeating what was said above (all of which I completely agree with) I would like to just mention a few things off the top of my head that might help you in figuring out some of the nitty gritty details:
Do you know enough to know how to choose teachers? Do you know the difference between a certification someone got by doing an online test that is not up to industry standard, and one that is nationally recognized? Can you take a class with someone and tell, not just whether the class is exciting, but if the teacher is doing potentially dangerous things, is sequencing properly, and providing modifications?
If a teacher were to have an emergency are you able to step in and teach? (without training and certification you would put your insurance in jeopardy)
What is the reasoning behind the things you list that you want to offer? Is it just that they share a lack of expensive equipment? Yoga does require some equipment: blocks, straps, mats, …. And even mat Pilates studios usually have some basic equipment: rollers, small balls, bands, for example. And the course of study and teaching requirements for teachers are different. And if you are going to do pregnancy yoga you need things like bolsters. I assume kick boxing you would need small amounts of equipment also. My point is, if you specialize in one area, or an area where the same things are used you won’t have the huge outlay for stuff.
You are planning to start to offer all these things at once? The marketing cost in time and money will be huge…. you are not even marketing to the same audience, so will have to have a plan how to reach different groups….and it takes time to build an audience.
How big will your space be?(What is the going rate for rent where you are? How many months can you afford to cover while you wait for classes to get full?) If you have only one room it will be hard to do each of those things…. for example the ashtanga style yoga is usually done in a hot environment, and if you are moving back and forth with kick boxing, or a pregnancy class you will be spending a lot of money on climate control. Keep in mind you are not going to open the space and have every class filled. There are months that get slow, and classes that won’t work, and so on
If you are planning to offer yoga keep in mind that the standard in the yoga world for someone ‘on the Alliance’ is a 200 hour training. Pregnancy yoga usually takes extra training. Pilates is different from yoga and has its own quite rigorous training program.
I am kind of getting ahead of things, but purposely, as it is important to see that there are a ton of things to consider before starting out.
Starting out by getting some sort of certification is assuredly the best place to start. You could, however, begin with running some numbers: look into costs: training for you, rent, equipment, salaries, heat, insurance, etc, talk to an insurance agent about insuring your space and your teachers (they should have their own, but you should have it also), see what the market is like, find out what the going rate of pay is, and so on. It is probably also a good idea to speak to your accountant as well.
If you are willing to put in the time and energy it is a wonderful thing to work in fitness/wellness. (a lot of work, but a wonderful thing) I hope it all works out for you.