I'd go with something like this:
1: Spellcasting
Like the Artificer, cantrips + 2 slots, half-caster for the rest.
Arcane armament
At 1st level, you wield a deadly arm using a combination of arcane magic and your knowledge of war. This firearm is called an Arcanist Brand. It is a ferocious weapon that can punch through armor with ease.
You are proficient with the Arcanist Brand and it use your Intelligence for the attack and damage roll. The weapon take the shape you want but is a-handed weapon that deals 1d8 damage (your choice of S/P/Band has the versatile (1d10) and thrown properties with a normal range of 15 and long range of 30. You choose a new damage type for the weapon when and it stays the same until you power it with another damage type. The damage type must be the same has the damage dealt by a spell you currently know.
As a bonus action on your turn, you can use one of the following option with the Arcanist Brand:
- Elemental Brand; You choose a new damage type for the weapon when and it stays the same until the end of your next turn. The damage type must be the same has the damage dealt by a spell you currently know. At anytime, you can change the damage dealt by your spellstrike features for the one from your elemental brand.
- Aegis of Warding; Your AC increases by 2 and you have resistance to damage dealt by spells and other magic effects until the end of start of your next turn.
- Arcane Bond; You weapon fly to your hand if it is within 60 ft of you.
If you lose your Arcanist Brand, you can create a new one over the course of three days of work (eight hours each day) by expending 100 gp worth of metal and other raw materials.
2: Thundering Spellstrike
You learn to channel thunder energy into your Arcanist Brand. As an action, you can make a special attack with your Brand that deals an extra 1d6 thunder damage on a hit.
This extra damage increases by 1d6 when you reach certain levels in this class: 5th level (2d6), 7th level (3d6), 9th level (4d6), 11th level (5d6), 13th level (6d6), 15th level (7d6), 17th level (8d6), and 19th level (9d6).
3: Archetypes
Choose: Spellwarden, Ghostblade or Arcane Charger
4: ASI
5: Extra attack
you can attack twice, instead of once, whenever you take the Attack action on your turn. Moreover, you can cast one of your cantrips in place of one of those attacks.
6: Planar Emissary
You have advantage to resist being charmed. You gain Expertise with Persuasion and Insight checks when dealing with creature of the Elemental, Fiend, Fey or Celestial type.
7: Archetype feature
8: ASI
9: Sage of War and Spells
You have advantage on all intelligence checks made to identify a spell. Moreover, once per round, you can identify a spell without using your reaction.
9: Spellstrike blast
You can channel force energy into your Arcanist Brand. As an action, you can make a special attack with it. Rather than making an attack roll, you unleash force energy in a 15-foot cone from the weapon. Each creature in that area must make a Strength saving throw with a DC of 8 + your proficiency bonus + your Intelligence modifier. On a failed saving throw, a target takes 2d6 force damage and is pushed 10 feet away from you.
This damage increases by 1d6 when you reach certain levels in this class: 13th level (3d6) and 17th level (4d6).
10: Archetype features
11: Improved Brand
When you use your Elemental Brand, the weapon ignore resistance to the damage type chosen for the brand. Furthermore, when you use Aegis of Protection, the AC bonus increases to 4.
12: ASI
13: --
14: Chained Spellstrike
You can shoot lightning energy through your Arcanist Brand. As an action, you can make a special attack with it. Rather than making an attack roll, you throw the Brand causing it to unleash a bolt of lightning, 5-feet wide and 30-feet long. Each creature in that area must make Dexterity saving throws with a DC of 8 + your proficiency bonus + your Intelligence modifier. On a failed saving throw, a target takes 4d6 lightning damage. This damage increases to 6d6 when you reach 19th level in this class. The weapon then returns to your hand.
15: Archetypes feature
16: ASI
17: ----
18: Bursting Spellstrike
You can channel fiery energy into your Arcanist brand. As an action, you can make a special attack with it. Rather than making an attack roll, you throw your Brand on the battlefield. The weapon detonates in a 30-foot radius sphere at a point within 90 ft. Each creature in that area must make a Dexterity saving throw with a DC of 8 + your proficiency bonus + your Intelligence modifier. On a failed saving throw, a target takes 4d8 fire damage. The weapon then returns to you hand.
19: ASI
20: Share the Brand
When you use Elemental brand or Aegis of Protection, you can share the benefit with every creature of your choice within 10 ft of you.
