Yeah you don't have to do IV's but honestly even if you don't like them its something you would get use to quickly. I don't do IV's. Ive tried a few times got a few missed a few. Obviously even without putting them in yourself you have to connect them, tape them, change lines etc but there is no blood and nothing to worry about. Inserting IVs is also something you might start with some experience not whilst your training.
Nurses and midwives often have something they can't handle. For me thats goolies. Make me heave or vomit everytime A bit embarrassing when you have to run at times.

As for shift work. Unfortunately you can't get out of it whilst your training. When your qualified you have more opportunities to say no to certain shifts and to arrange set shifts that suit your needs. Unless your in management or community health then you nearly always have a 7am start from a morning shift not 9-5. But every hospital is different and the bigger the hospital often they have more variety in start and finish times.

Working on a casual basis you have more flexibility (although no guaranteed work) you can refuse to do night duty and evenings and just work during the day.

How do you find placenta's looking through them for abnormalities, checking the vagina for tears, poo, vomit etc? If that doesn't worry you then I am sure you will be fine. Even with a weak stomach you can still be a midwife if thats the profession you want to do. Also some places do not take direct entry midwives. You actually have to become a registered nurse first then do midwifery. Thats another thing to consider. Do you want to do general nursing first in order to be a midwife. I would recommend doing both as then you have two qualifications and really it depends on where you live as there are not alot of universities who run the direct entry midwifery.