Spell slots, Eldritch Knight / Arcane Trickster build (+ Feedback)

[Menagroth]

Question: Regarding the spells slots for the multi-class Eldritch Knight / Arcane Trickster. Do you add up all the levels and THEN divide by 3 or do you do each class separate? Seeing how at one point I will be level 5 fighter and level 4 rogue. This would mean I could be level 2 spell caster (5/3 rounded down is 1, and 4/3 rounded down is 1, for a total of 2) OR I add up all the levels to 9, then divide by 3 giving me level 3?

Feedback:
Looking for general feedback if anyone sees any glaring holes in the build. I am aware this is not a meta-max character, but if there any real problems or improvements to be made I am happy to hear them.

Theme:
I have been messing about with this for some time, been having fun trying to figure out different combinations. Basically its a bit of jack-of-all-trades by maximizing the number of feats/ability score improvements I could take, and spreading skills out by multiclassing.

As I see it:
Pros: High AC, Good offensive and utility abilities. Rogue like skills with front line staying power, and the ability to throw spells around.
Cons: Multiclass means less impressive high level skills / abilities, spells don't necessarily mix well.


Race: Human (Variant)


Starting Stats:

Str 11
Dex 16 (15+1)
Con 12
Int 16 (15+1)
Wis 10
Cha 8


Equipment:

2 x Rapier
Dagger
Handaxe
Light Hammer
Breastplate or Halfplate with Medium Armor Master


Feat List

Feat # | Character Level | Feat Name
1 1st Dual Wielder
2 5th War Caster (Replaced Defensive Duelist)
3 8th +2 Dex (18)
4 10th Alert
5 14th Resiliant +1 Dex (19)
6 16th +1 Dex, +1 Int (20Dex - 17Int)
7 18th Observant (18 Int)
8 20th +2 Int, Dungeon Delver/Lucky/Medium Armor Master/Mobile (Not sure which to take?)


Skills:

Human: Perception
Fighter: Acro and Athletic
Criminal: Stealth and Deception
Rogue: Investigation and Thieves tools


Proficiencies:

Perception (Expertise)
Investigation (Expertise)
Stealth (Expertise)
Thieves Tools (Expertise)
Acrobatics
Athletics
Deception
All weapons and armor, shields


Cantrips:

EK: Fire Bolt
EK: Mending

AT: Mage Hand
AT: Minor Illusion
AT: Light
AT: Booming Blade


1st Level Spells:

EK: Grease (with Firebolt = fire trap, lure enemy out with minor illusion then set them on fire)
EK: Shield
EK: Absorb Elements
EK Chromatic Orb

AT: Disguise Self
AT: Charm Person
AT: Find Familiar


2nd Level Spells
EK: Darkness
EK: Hold Person (8th level spell)

AT: Mirror Image
AT: Invisibility
AT: Suggestion
AT: Darkvision (8th Level Spell) (synergy with Darkness)


Level Progression:

Level 1 fighter: Fighting Style: Defense, Second Wind, Dual Wielder
2: F1 / Rogue 1, Expertise: Thieves Tools and Investigation
3: F2 / R1, Action surge
4: F3 / R1, Eldritch Knight (Bond Rapiers; Fire Bolt, Mending; Shield, Greese, Absorb Elements)
5: F4 / R1, War Caster
6: F4 / R2, Cunning Action
7: F4 / R3, Arcane Trickster (Mage Hand, Light, Minor Illusion; Disguise Self, Charm Person, Find Familiar), 2d6 Sneak attack
8: F4 / R4, +2 Dex
9: F5 / R4, Extra Attack
10: F6 / R4. Alert
11: F6 / R5, Uncanny Dodge, 3d6 sneak attack
12: F6 / R6, Expertise Perception and Stealth
13: F6 / R7, Evasion, 4d6 Sneak Attack
14: F6 / R8, Resiliant +1 Dex
15: F7 / R8, War Magic: Cantrip + Weapon attack as bonus
16: F8 / R8, +1 dex, +1 int
17: F8 / R9, Roguish Archetype, Magical Ambush, If hidden enemy has disadvantage on spells, 5D6 Sneak attack
18: F8 / R10, Observant +1 Int
19: F8 / R11, Reliable Talent
20: F8 / R12, +2 Int, Dungeon Delver/Lucky/Medium Armor Master/Mobile

Thanks for having a look :)