I don't think it has to be considered a min max munchkin build if you role play a design.
SOU Hotu is a fine trial run. Take the same character onto some of the community post HoTu mods that are available at higher level.
The basic premise is 3 levels of Paladin stacked on your Sorcerer build to obtain the armor / weapons feet. Build charisma steadily to improve your paladin and sorcerer feats. More or less Paladin levels is a "choice" not a mandate though the 3 is generally accepted as being "enough".
Of course you also need to account for the fact that your need to gather the meta magic feats that allow you to cast in armor without spell penalty chance (Still cast IIRC) ; further you wont achieve these all these feats till at least around level 9 IIRC depending upon other selections ~ meaning you wont be able to cast your highest level spells in armor till mid teens when 7-8-9 become available anyway.
The heavy armor does not really get your AC high enough to be "game changing"... you are still using your spells to (1) minimize damage i.e. ghostly visage or improved invisibility or (2) take down opponents with reciprocal damage spells i.e. acid sheath. Stoneskin as always.
However the weapon proficiency and armor should allow you enough flexibility to wade into weak mobs of orcs / goblins without too much concern.
But in terms of concept nothing wrong. You can play most single player mods with this type of build - use the build link above to see better alternatives and progression.
Consider to be a Paladin or Divine champion of Mystra build for example. Would not the mistress of the weave indeed promote a spell casting champion ??