Should the Tung oil be thinned with mineral spirit for the first coat? Or you would recommend applying it pure.
Never with mineral spirit - too toxic and smelly for bees. You can apply it neat, it is just harder work for the first coat. I diluted mine 1:1 with food grade Citrus Solvent (also called D-Limonene), making it easier to apply and faster to penetrate the wood. The second and third coats were pure Tung Oil (no thinner).