It's difficult integrating new skills and knowledge, adjusting to a culture differences AND learning a new language all at once. Try an get as much Spanish under your belt before you come and use your time here learning midwifery. This money helps support the overall project. Other expenses include room and board. Spanish schools are plentiful in Antigua.
All schools provide one on one instruction for any level beginners through advanced.
Costs vary and are usually approx. The sooner tickets are purchased the cheaper they are. A passport is required to enter Guatemala and they give you a 3 month visitor visa when you enter the country. There aren't a lot of weird tropical illnesses although Dengue has been reported in areas of Guatemala. Antigua is relatively safe and the infrastructure is good.