Some thoughts about weights:
I am fortunate to have a 4, 6, 8, 12, & 16 lb Shovelglove. ( The 4 & 6 were purchased in a burst of zeal when I realized how much I enjoy shugging-that's the verb we use, yes? - and wanted my young sons and wife to develop the habit as well.)
When I searched posts about weights IIRC I saw one by Reinhard where he said that he used a 12 for some time, (approx. 1 yr.?) and then moved up to 16, but still picks up the 12 from time to time and, again IIRC, the term he used that most impressed me was about his not moving up until he "owned" the weight.
Before I went on my SG buying spree, I already owned the 8 & 16 that I rarely used for tire striking work. The idea of "domesticating" the sledge with an old sweater

, and doing other movements, regularly, indoors, really clicked for me. The traditional movements help me get through the mental/emotional inertia of just getting started by simply picking up the SG and just start shoveling, then chopping, then churning, then ab killers and variations, then some non-canonical moves really get me rotating and moving.
Back to the "what weight" topic: Without knowing your strength & conditioning level, it is hard to say precisely. My guess is that an 8 or 10 should work fine no matter what, and here's why.
I have been cycling through all the weights, and I love that. I think it (cycling,) is healthy for mood, sustained interest and physiology. Mostly I use the 12, and then the 8 & 16 about equally, but I've even played with the lightest ones. When I use the 8, I MOVE. Fast shoveling and chopping! The 16 is slower and deliberate. Some days the 12, a'la' Goldilocks, "is just right". However with the light ones, I can do movements that I can not with the 12 & 16, or can not do as gracefully with even the 8. For example, moves that approximate, ( with grip-leverage variation,) baseball bat swings, etc. Also, after a few days with the heavier weights, when I return to a lighter one, my "owning" of that lighter weight and my ability to generate either more intensity or greater grace/control of movement with the lighter weight is noticeably greater. Interestingly, after greater intensity with the lighter weight, I feel that my strength is somewhat greater when returning to the heavier weight.( Although the latter is not always true. Sometimes heavier just feels heavier.)
So, bottom line, jump in with a 8 or 10 and depending upon your feelings as you go along and your budget, ( a hammer is pretty inexpensive as "lasts forever" fitness equipment goes,) consider adding other weights for variety.
BTW, as I do a number of non-canonical movements, a vendor is preparing a hammer weighted on both ends, ( initially 5lbs each side,) that I am going to experiment with. If anyone is interested I will report back at some point as to my experiences with same.
Happy Shugging Simon B. !
All the best,
Eddie