1)
Regarding what did he not heed the nation?
1.
Radak: Above, they requested to lighten the yoke on them.
2.
Malbim: There were more arguments between them. They showed that one does not rule over a nation against its will with a staff of Chovlim. He should have seen what the end will be, and heeded them.
2)
Why does it mention his Nevu'ah about Yaravam? Is it not more appropriate to mention his Nevu'ah that kingship will be taken from Shlomo's son (11:35)?
1.
Malbim: The latter Nevu'ah is bad for Rechav'am; it could change if he improved his deeds. However, since the Nevu'ah included benefit for Yaravam, it is absolutely guaranteed to be fulfilled.
