Getting started as a hotwife/cuckold couple is best achieved by introducing role play in the bedroom to establish this as something shared between rather than something she does on her own.
From there, the talk of her being a hotwife should extend outside of the bedroom; quietly ask her which men appeal to her when around others. Ask her which one she’d go on a date with. Make discussion of such things seem a matter of when, not if.
Next: To become a hotwife, your wife should adopt the persona of one. This means dressing and behaving as a married woman who is sexually available and obviously interested in male attention.
From there, nature will take its course with men approaching her and the usual courting behavior taking place, but this time, she’ll have you to share it with and together, you’ll choose a path forward.