It's once every
several generation
s for a race that lives on average to 150. Multiple generations, not one. I was assuming a generation was 50 years because of the lifespan. None of the lore really explains when they start having families so it's just what I would do for my home campaign.
There's no reason for halflings to not use weapons, the book doesn't forbid it. As with most races it doesn't really go into it. The same way that commoners of all races will use the best weapon available not just the
stick clubs listed in the MM.
There's also no reason they wouldn't have guards, veterans and so on although with 100 people or less it's not particularly likely.