Interestingly enough, the yen is written in front when you use the yen symbol that's internationally recognized, as in ¥1000, but locally in Japan they often put the word for yen (円) on price tags instead, and that goes after the number, as in 1000円.
Not very often - i'd bet under 5% of even handwritten instances in Japan, and feels like it would be an elderly person who wrote it (hardly narrows it down in jp tbf).
Nah, very common, and not just handwritten either. If you image search for 値札 (price tag) you get tons of results with the 円 version like below. I see it all the time in stores.
I'm sorry, but you're simply wrong. For example, every conbini in the country has virtually all their goods labeled with 円 instead of ¥, which alone is tens of thousands of shops. I dunno if you ran into a few weird shops in your time in Japan, but I'm telling you that daily life here involves way more "en" than "yen".