If I register a personal e-mail adress for a new external registration, are e-mails sent to my company’s email as they’ve been? Also, does it affect on the linkage with daily step count?

If you register a personal e-mail address, that is proioritized over your company’s one, so the e-mail will be sent to your personal one from that point onwards. There is no problem with step linkage. The same number of steps will be shown whichever e-mail adress you log in with.