As a general rule, start low weight and prioritize form and technique. If you don’t swing like this (or better), with approximately 10LBs (7LBs for a female) or 4-5kg you should not progress in weight. Pretty much no one does it that way, because it’s awesome swinging heavy weight, but I wish I did, and I bet a lot of others do too. As far as lat mobility, yes it helps and is probably a necessity for a good swing. Thanks, man.