Dear Seamoro,
It is good to hear that you are determined to carry on with your education and to work in the endless field of the plant science.
I'm at your age exactly so maybe my opinions aren't still "experienced" compared to some experts here on the forum. But I would like to write here my 5 cents...
When I started with my MSc thesis couple years ago, I have the same "idea" as you in my mind. I come from a country that has a wide variety of plant species that are used in traditional medicine but are unknown or partially known to the exact science and medicine when it comes to their composition or in vivo activity. I'm currently working on different "idea" which is faaaaaaar away from my initial "idea", but that's the way life goes. My colleague from the university has the opportunity to do his PhD work that is very similar to your future science intentions, so speaking and observing the job that is required to be done I can comment a little bit in order to help you in some way.
Anyway, your chromatographic experience will help you to separate the compounds from the plant extracts and to obtain them in preparative manner to be able to submit them to MS, IR, NMR, DSC... analysis as pure compounds (if you want to elucidate their chemistry). But before chromatography you should do a lot of sample preparation, a lot of different extracts (ethanolic, hexane etc) depends on what type of compounds are you looking for in the extracts (volatile, semivolatile, nonvolatile, polar, semipolar, nonpolar etc).
Also when you'll obtain your extracts or pure compounds (for which a lot of prep chrom. work will be needed) you should be prepared and trained to apply the bioactivity tests on cell culture or on alive animal models (I don't know what you're intentions are, so I am more general in my elaboration). Get familiar with those tests before you start to plan your experimental work, because the work with live animals can be a nightmare for inexperienced scientist.
For the 4 year (i suppose) PhD period you should be able to do a lot of your PhD work, but only and if only you're focused from the beginning of your PhD on one chemical group of (potentially) active plant chemicals (with that said, you'll need to do a thorough library/article research before you determine your target compounds)
Get informed about the traditional usage of the plants you're going to include in your PhD work. And if you're not familiar with the culture and the tradition of the local people (I suppose you are planning to get your PhD in Sout East Asia) talk to the PhD students who already do the same or similar research in the area where you're planning to settle for your PhD studies.
Be aware that choosing the plant material as main research sample will cause you a lot of headaches but the beauty of the PhD work is to learn a lot and enjoy the "ride", but also get the problems fixed as soon as possible
I wish you a lot of success in your future research plans and work.
Best regards,
Zoran