I'm not Taiwanese but I travelled there in 2018 and can answer:
- Google Maps is recommended, OpenStreetMaps based solutions were generally not recommended.
- I either used Chunghwa or Taiwan Mobile, not sure, I got setup in person at a retail outlet around the harbour in Keelung City, 1 person spoke some english and was able to get me sorted. Later on I was in a more rural area and didn't have any retail outlets around me, there was 1 provider that had machines you could use to get a SIM in the local 7-11 but I needed to get a local to help me with it due to language barrier. Nowadays E-SIM is a thing so look into using that instead if your phone supports it, mine doesn't.
- Elephant Mountain by new taipei. Taipei night markets. Taroko Gorge. Sanxiantai Island. The warehouse bar in Hengchun if it's still around. That big rock that looks like an elephant by the coast near Keelung. Juifen town. Dulan beach. They used to have live shows at the Sugar Factory in Dulan as well.
- Accommodations were affordable and plentiful in the western, urbanized, part of Taiwan, but everyone tends to converge upon Taipei for the weekends so plan ahead or you might have a hard time finding a place. Same goes for holidays. During the week I could pretty much just walk in to wherever I wanted to stay.
- Scams are basically non-existent, there is no where in south or east asia I would consider as integral as Taiwan in this regard. My experience is you will always be charged a fair price and no one will try to rip you off. In terms of natural dangers I was only warned of Venemous Snakes if out in the bush, and of course you are on an island so beware of the possibility of sudden typhoons and storms. Earthquakes are a possibility.
- The further you get away from Taipei the harder it will be to get by with only english, but I managed so it's doable.
Overall a very underrated country for travel when you consider cost relative to safety, ease of transportation with trains going around the whole island, and fantastic food.
