Default [Q] Rooting and security issues:

As a phone noob who is interested in rooting my GT-i9305T, it came to my attention that i trade stocks frequently from my phone and also bank online from my phone.

Does rooting present any security risk to these activities?

I have both read and heard that rooting a phone takes away security measures (whatever that means?). If this is true, how much do i need to know in order to make my phone secure while performing these activities?

Is it a serious risk to root the phone, download after-market apps and at the same time access private financial information??

I have heard the saying that an operating system is as safe as the person using it. I guess this goes for android phones as well, but how much do i need to know exactly?