You can make new EC or unrelated ECs in same book, whether its plain or ruled page it doesn’t matter. Yes you can charge only that particular page as you want.
Don’t put two different ECs/person/situation on particular left and right pages , because if you keep VK on one side(say left side page ) and close the book, the other side(right side page) written words will also touch VK.
Though you can use the 2015 diary ….
Personally i feel the book for healings with VK should be separate, you can carry it even while travelling or at work or even at vacation.
If you have different aspects/ECs/people to be charged on different pages, it will also help you to schedule your healings. It will be a daily reminder for you …..what all you need to heal regularly.
I have a healing book only for VK, on the first page i have written GOLDEN SUNRISE OMSAIRAM , it gives me a FEEL GOOD FACTOR when i start or continue healing.