First of all, let me commend you for your desire to learn and practice your faith. I pray to Allah to bless you in your efforts to remain steadfast.
Now coming to your questions:
1) Islamic guidelines in regards to modest dress for women do not prescribe niqab (face veil); therefore, it should certainly not pose an obstacle in your path towards achieving your professional ambition;
2) Likewise, it is not essential for you to wear an abaya or any particular style of dress; what is most important, however, is to wear modest, non-revealing clothes that cover your body except the face and hands. Furthermore, Islam also values safety and protection of life and health as the top priorities; as such, being in a medical profession, you are allowed to conform to the standards set by them-as long they do not contravene any of the fundamental principles of the shari'a. According to the best of my knowledge, it is perfectly acceptable for you to comply with the regulations you have mentioned above.
3) As for the mixing that is unavoidable in the work setting you are in, it can be excusable-as long as you take care to shun isolations, and guard your speech and eyes, and remain focused in your work, while trying to guard against the whisperings of the Devil by arming yourself with dhikr and du'a.
4) It is essential that you venture out of your home with the du'a of protection against the Devil; here are two du'as you should practice on a daily basis:
Bismillaahi tawakkalthu 'ala Allaahi laa hawla wa laa quwwatha illaa billaahi
Allaahumma inee a'oodhubika an azhilla aw uzhalla aw ajhala aw yujhala 'alayya
(In the name of Allah, I set out from my home, while placing my trust in Allah alone; there is no power to resist evil nor strength to gain virtue except by the will of Allah.
O Allah, I seek refuge in You from going astray or being forced to be led astray, or acting foolishly, or people acting foolishly towards me).
I pray to Allah to help you achieve your professional goal, while seeking the pleasure of Allah in your work.