Yer becoming a mechanic already
. Yes the nut should be fine. It is a good idea when replacing nuts, bolts or studs to get Grade 8 when you can. They are stronger heat treated steel and rust far slower than softer ones. Stainless is not a bad idea either in some cases.
In "ANY" T'stat installation first determine whether the "recess" for the flange of the T'stat is in the block or the housing, that is where the T'stat should be first and the gasket between the housing and the block.
When the T'stat is in the housing you can use a bit of Permatex to hold it in place so it does not fall when inverted in hard to reach installations. It is also a good idea to goop both sides with a film of Permatex for best sealing. The silicone style sealants work well on new and pristine parts however the Permatex will not allow moisture in as the oil saturated in cast iron will not allow the silicone to bond to the metal. Silicone works well on aluminum though and Permatex will stick to both. Permatex #2 or "aviation" grade are well proven.
Dave Neptune
