Plants and seeds can be sold on ebay UK, provided they are located in the UK and not endangered species, or prohibit by the law or by carriers rules.
You can find the ebay Plants and Seeds policy here: Plants and Seeds Policy
If you would be producing seeds and cuttings specifically to sell, it would need a business account because you would be trading. If you are just selling off a small number of plants, cuttings or seeds left over from your own usage, probably not.
Regarding plant passports, you can read up about the requirements on the following gov.uk webpages:
DEFRA plant health portal
when-you-need-a-uk-plant-passport
list-of-plants-plant-products-and-objects-which-need-a-plant-passport-for-movement-within-gb/plants-...