These mixed companies can be very confusing to tourists especially. I'm always answering questions from tourists who are confused why they can't buy a ticket to where they want to go.
Almost everything works with Suica, no? Although to be fair I guess tourists are _more_ likely to use the heritage lines with slightly different rules.
It's basically one card for everything, independent of company, in Japan. Only certain trips require tickets from specific companies.
If you intend to do a fair amount of travelling and your stay is <3 weeks, it may be worth getting a JR Pass[1]. It doesn't work for all lines, but does include the Shinkansen and several of the major inner-city lines. Buses too.
Probably not worth it if you're only visiting one city as the pass is quite expensive. There are regional tourist passes though.
[1]:https://japanrailpass.net/en/