Here's my direct unofficial answers to your questions.
1. I guess you can - provided you have not taken any scholarship
payments for your tuition fees, etc. You will have to pay back
everything you have taken from MINDEF.
2. What's your current education level ? It depends on whether
you sign and get sponsored polytechnic education, or you are hoping
to get scholarship to further a degree course.
Do note that they have very strict and narrow list for courses
they will award scholarship for.
3. Regulars can continue indefinitely until their retirement
age, provided their work is delivered at least satisfactorily. (ie.
if you are charged for offences, lazy bum, etc. you may get
condemned and not get renewed, or even early discharge;aka
fired).
4. Combat medics are basically battlefield medics. They are
trained to a high degree of proficiency and first and foremost
expected to be combat fit (ie. you need to pass IPPT/SOC and combat
medic course, physically fit to carry stretcher, etc.). There are a
handful of female combat medics.
Afraid of blood, then very difficult. I guess it will be
difficult even to be a civilian nurse...what more a combat medic.
In wartime and even peacetime training, they are expected to be
relied on to treat casualties, including trauma casualties from
accidents, gunshots, broken limbs, etc. If you are afraid of
blood....I don't know how you can cope.
Also they have to be certified regularly to handle CPR, IV drip,
etc.
How about you consider another vocation?