Pregnancy planning. We start trying?

I am 29 Years old, Female. I’m planning to start trying for pregnancy from October and this would be my first pregnancy. My menstrual cycles are usually regular, around 29–32 days, and I don’t have any significant medical history. I’m confused about the different folic acid doses available, such as 400 micrograms and 5 mg. Which dose would be appropriate for me, and when should I start taking it and at what time of day? I have also gained some weight recently, have borderline cholesterol, and my vitamin D level is low. Should I take vitamin D or any other supplements before trying to conceive, and do I need to correct the vitamin D deficiency first? Could you also advise whether I need any other preconception blood tests or supplements before we start trying?