score:5
The easiest way to find out whether Suica et al. can be used at a JR East station is to type the station's name in Japanese (with the suffix 駅) into a search engine, and look at the corresponding 駅の情報 (station information) page on the JR East website, which should be among the first results. See for example here for Aizu-Wakamatsu station.
The station information page contains a Suica section with four "boxes", which indicate (from left to right) whether a Suica can be
If the box is green, yes, if it is grey, no. If the page does not contain a Suica section, it means no to all.
For non-Japanese speakers, a simple way to obtain a station's Japanese name is on the line's Wikipedia page (for example here for the Ban'etsu West line), which lists the line's stations in Japanese and Latin characters.