ᐅ Insulation of the top floor ceiling, followed by insulated roof sheathing?

Hello,
I am currently renovating a semi-detached house and have removed the very old insulation wool from the attic. Now I am considering insulating it again. Whether the attic is walkable or not, what happens if in 5 to 10 years the entire house is renovated with an insulated roof overlay? Will I have a big problem if I install a vapor retarder on the ceiling of the upper floor now, and the roof is insulated later? I am leaning towards a non-walkable attic with wood fiber boards without a vapor barrier underneath. But even here, the question is what happens if the roof is insulated and the attic becomes "warm," though still unheated? Should I expect moisture and mold issues, or will the roof be insulated with a variable vapor control layer? So many questions. How should I insulate the attic now? For 5 to 10 years without insulation, the indoor temperature would be too cold/hot for me. Thanks for your advice!