Start Draconic Sorc for Con saves, then take 2 levels of Tempest Cleric, then all Sorcerer from there.

Cha is king. Get it to 20 ASAP. Wis and Dex can stay at 14 forever. Wear Medium armor and shield, but keep one hand free always. Warcaster isn't necessary.

Transmute spell metamagic is a must. Metamagic Adept feat helps get you back the 2 Sorcery points you lost by multiclassing. Elemental Adept isn't completely necessary since you can toggle between lightning and thunder damage, but it wouldn't hurt.

That's all you really need. Possibly later on in your career once you're Sorcerer 14, Cleric 2, you can debate between having your highest level Sorcerer spells vs going Cleric 6 for a 2nd use of Destructive Wrath per short rest. Honestly this feature is so awesome it just may be worth giving up your 8th and 9th level spells slots to double the amount of max damage lightning/thunder spells you can dish out. You would end up with more spells known I think going Sorc 14/Cleric 6, but you'd only be a 7th level spellcaster. Sorc 18, Cleric 2 is probably better overall even just for Wish. You'd have Dragon Wings either way and the 18th level Draconic feature is "meh" for you.

For races, Blue Dragonborn is most fitting.
Dwarf would let you wear heavy armor while still dumping Str.
Custom Lineage or Vhuman starts with a feat lets you start right off with Metamagic Adept which is awesome.