Look at where you are and also what else is available so you're not in direct competition and offer something specific and unique above the normal range of fruit and veg expected. Agree with NFD that a focus on local produce is better than trying to mimic supermarket range of imported varieties, and for me a coffee shop is a must as a draw. I frequent several local farm shops regularly rather than just one, as they all have strengths and weaknesses and I also don't like to get bored so you aren't competing in prices, but in being a new variation on the very popular theme.
I have had plans to do exactly this kind of project for several years, but not with the current property, so it's been a factor of places I've viewed in the past to come up with what each one could do and every property is different in what you can develop there so know your property, know your area and your market and start with a couple of things you can manage, leaving scope to expand and develop rather than try and do it all in one go and end up with second rate overstretched resources.
Local crafts is always a winner and doesn't involve you in direct work other than the till sales you are already manning so it makes sense. It also gives you an audience of friends/family of all the crafts folk for your coffees and folk to tell their friends to come and look.
The quality of your coffee and home baking is probably what will make or break you so don't skimp there, along with the attitude of any part time staff you employ and the comfort/attractiveness of the cafe area, carparking convenience for wet weather, disabled facilities a must obviously, but go the extra mile and folk will repay with loyalty - so also change some of the menu occasionally but keep a strong base of regular items that are top sellers as some folk like the same thing time and again and others like to try something different.