Does anyone have any advice on choice of PhD project in bioinformatics/systems biology?

I have a degree in chemistry and masters in mathematical and computational ecology. However I have since then become much more interested in bioinformatics and computational molecular biology. My academic background in these areas is limited though, so I am not sure if this change can be made without another masters.

Does anyone have any advice on making this change and things to look out for? I'm particularly interested in whether another masters is advisable or whether this conversion is done regularly without one.

I also have an eye on post-PhD employment opportunities. This is important as I am 30 and will be giving up another career to make this change so I need to be mindful of the career it will lead to longer term. Are the skills from most PhDs in this field sought after, or are there areas that are hotter than others in terms of prospects?

Apologies for the length of the post! Grateful for any advice.