Grocery stores are probably not the best place to look for pallets since most of the pallets they get must be food safe and therefore expensive. Look for pallets at nurseries or any of the so called dollar stores or other businesses that recieve non edible products in large quantities. Keep in mind that to keep from having these items pile up many of these stores may have a contract with a company that makes mulch to haul them away.

Well the first year in the greenhouse has been going ok we have over 1000 starts on the table. The 4mil free plastic I got from a friend is hard too keep the wind from blowing it off, so I've had to reattach it a couple of times, so I entend to invest in clear corrugated roofing next year. Even though we have mild winters it still would be nice to have a heat source for the couple of mounths it gets cold so I'm thinking of building a rocket mass heater. Anyway thanks for all your feed back its motivating me to build more.

25 Square feet is not very big. Would decomposed granite work? You could add seating & container plants. what are your goals for the area? https://www.houzz.com/photos/fire-pit-traditional-patio-chicago-phvw-vp~3583545?share=clipboard

For a Scandi feel I would paint the walls white. Instead of removing the wood surround I would try painting it the same color as the walls. It "should" provide you with some interesting texture once painted but shouldn't stick out like a sore thumb. If you don't like it once painted would suggest you just remove it and replace with a more traditional surround with a mantle. Would also suggest hanging artwork that has an appropriate look above the fireplace once painted. Good luck!