I'm looking at the cost/reward of the taking a 2 level dip in Evocation  Wizard for the below

Sculpt Spells

Beginning at 2nd level, you can create pockets of relative safety within the effects of your evocation spells. When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures automatically succeed on their saving throws against the spell, and they take no damage if they would normally take half damage on a successful save.

The initial cost is 2 levels lost in progression in your main class. 

• 1 Full level of spell behind normal progression
• 2 Levels behind Ability Score/Feat progression
• 2 Levels behind for Class Features.
• (Edit) Makes you MAD. - Depending on if you Roll (and what you roll), Point Buy or Standard array your inconvenience will vary. 

The benefits i can see are

• 6 Extra Level 1 Spells/Int +2 Prepared (And the ability to learn more)
  
  • Assuming you're planning on taking Shield,  Mage Armour, Absorb Elements or  Slivery Barbs. You can take these in Wizard instead of Sorcerer to "Get these back" as Charisma does not effect these.
  • However you also lose 2 Extra Spells known of up to your max spell level, that you would have gained by taking 2 Sorcerer levels 
  • Most Sorcerers however, will take at least 2 form the initial list if not all 4, so you're between 0 to 2 extra Spell choices available to you. 
• 3 Extra Cantrips 
  • Again you can take Non-Cha Cantrips, Mage hand etc 
• Bringing the Boom!
  • While you can take careful spell almost all AoE spells your Allies will still take half damage (see below) and it doesn't cost any Sorcery points.
  • This can be a bit group/player dependant. Some players groups will be unhappy if you damage there characters. And we should be making sure everyone has fun, not just us. What do we do if one player says "don't use fireball if it will damage my character"?
  • What use therefore is an amazing spell that we never or rarely get to use.
  • Removes the cost/benefit calculation even if there are more Players and NPCs in the blast radius. 4 NPCs but 5PCs - Upcast fireball to 4th Level and boom!

  For me the "What use therefore is an amazing spell that we never or rarely get to use." is perhaps the biggest point. However never getting the spells is also an issue.
  I would suggest level 6 to 7 would be the best time to take the Wizard Levels. As third Level is where a lost of great spells come along, including fireball. 
  So why not just play an Evocation Wizard then?
  This is the hardest question to answer. Not wanting to,  wanting only the Sculpt Spells feature form the Wizard class features along with features you can only get from going deep into Sorcerer. More than 2 Meta Magics Slots/Options for example.

  Careful Spell 

  When you cast a spell that forces other creatures to make a saving throw, you can protect some of those creatures from the spell’s full force. To do so, you spend 1 sorcery point and choose a number of those creatures up to your Charisma modifier (minimum of one creature). A chosen creature automatically succeeds on its saving throw against the spell.

I would almost never upcast fireball for an extra 12.5% damage it isn't worth the higher slot. My druid does sometimes upcast moonbeem but that is doing an extra 50% damage comparing level 2 and level 3 (33% extra comparing level 3 and level 4).

It isn't just 3rd level spells, a lot of other spells have the biggest impact when they are first available and with two levels of wizard you will be getting them two levels late that is a significant disadvantage.

Fireball is best used in the first round of combat before the melee characters have got mixed up with the enemies and the enemies have not spread out to fight the various party members.

A big disadvantage you haven't mentioned is multiclass into wizard makes you MAD. A sorcerer needs high Cha and decent con and dex.  Wis is an important save and perception is important so you probably don't want to dump that but you can dump Int and Str. To take levels into woizard you need 13 Int which usually means your Con or Dex suffers. If I was creating each character using point buy and a +2/+1 race I would probably go:

• Pure Sorc:   Str 8, Dex 14, Con 15+1, Int 8, Wis 10, Cha 15+2
• Sorc / Wiz:  Str 8, Dex 14, Con 13+1, Int 13, Wis 9, Cha 15+2 (if carrying capacity matter I might put 9 in str but this keeps the comparion simple  

The net result is you lose +1 to your modifier in both Con and Wis, the two most important saves in the game especially for a spellcaster. You gain +2 to Int but unless you are fighting a lot of mind flayers that will rarely come up. While you could get the wis back with a split ASI at level 4 you are almost certainly better taking a feat like Fey touched, telekinetic (if you don't take quickened) or skill expert to get your cha to 18.

Regarding "bring the boom", I would almost never upcast fireball, for an extra 12.5% damage it isn't worth the higher slot. My druid does sometimes upcast moon beam but that is doing an extra 50% damage comparing level 2 and level 3 (33% extra comparing level 3 and level 4).

I've played both evoker and Divine soul Sorcerer. I like both, but would not combine them. I don't see any reason to put points into both INT and CHA. You'll probably already be putting points into CON and maybe DEX as is. I can see (for a new character) going loxodon or tortle and changing stat bonuses so as not to focus on DEX, though (to better focus on CHA and CON).

I always plan multiclass levels at character creation, so i have a level 1 twlight cleric, level 13 Evoker that I really like....who can wear mithril plate armor.

I voted no, because you miss out on an ASI, and also one of the Metamagic options is careful spell, which means you can achieve your goals without multiclassing. Also with the dip, you would miss out on the sorcerous restoration feature, which is pretty good.