How to give my kitchen table a farmhouse look?

You need to lightly sand the top. Then prime, Then paint or stain. If you use chalk paint do not use a wax finish on the kitchen table, Use poly acrylic in several coats. It will last longer.

Great table for staining and chalk painting! I would stain and poly the top first. As far as preparing the table top--you would need to strip/sand any poly on the table top before you could stain it. General Finishes makes a gel stain that doesn't require much sanding but I prefer staining with regular stain and then adding poly. And if the legs have any poly on them just give them a light sanding to know down the shine before you chalk paint.

It does not matter what order you paint and stain. Just make sure you poly whatever you are painting with the chalk paint. Wax makes a greasy mess on a table or in the kitchen eventually. Sooner not later.

If you use a gel stain, you can just sand the table top before applying it. I would do the top first, so if you have any drips onto the legs, you can just sand it off and then paint the legs. Here is a tutorial of something similar to what you want to do:

https://www.minimalishfarmhouse.com/blog/2018/1/25/dining-table-overhaul