Re: land a new job, or launch a new job?
I would not use "launch" that way.
If you create a new business, you can launch a business. If you create a new product, you can launch a product. Launch does not work well with the idea of a job, especially one that you are doing instead of creating.
If you, yourself, have recently "landed" a job, I suggest you simply say you are starting you new job.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.