Would this be legal/practical? Swashbuckler/Sorcerer Multiclass

[Abenadia]

So I've been looking around, trying to find ways to make playing a Swashbuckler rogue interesting. I found that some people take Magic Initiate as their level 4 bonus to get Booming Blade, which has great synergies with a rapier build. The problem I found with this is that unlike a dual shortsword build, your offhand is getting pretty much no use. I found the sorcerer bloodline of Stone Sorcery in one of the Unearthed Arcana, and it seemed to fit what I was trying to do perfectly. For those who have not read it, Stone Sorcery is designed to provide an option for a melee focused sorcerer, adding several Smite spells to the learnable list at early levels and giving simple/martial weapon and shield proficiency at level 1. The questions I have about building a Swashbuckler X / Stone Sorcerer 1 character are as follows:

Would Stone Sorcery give shield proficiency if it is chosen as the secondary class? Every other class that gives an armor proficiency also gives it as part of multiclassing, but sorcerers normally have none.

Would the interaction of Smites and Booming Blade work as follows: Move in to attack enemy, use bonus action to cast a smite such as Thunderous or Searing (smites cost 1 bonus action), use Booming Blade as the 1 main action of the turn, if the attack lands it will trigger both the effects of Booming Blade, the normal attack damage, and any damage and effects from the Smite, and Sneak Attack IF all normal conditions are met.

Sneak attack working off of Booming Blade: I have read that because Booming Blade triggers a melee attack action, sneak attack should work off of it as normal. I would like additional confirmation that this is the case.

Wielding a shield in my offhand: If I am correct in my assumptions, I should be able to use a shield in my offhand with no problems due to proficiency, and due to the required components for the spells I want to use being Verbal and Material (Sword) for Booming Blade, and Verbal only for Smites (how else are paladins going to cast them anyway). My total AC should be 10 + DEX + Light Armor (1 or 2) + Shield (2).

And finally: If all this works, it is practical? I am playing a campaign that starts us off at Level 4, homebrew and UA allowed, and I really enjoy the flavor of a swashbuckling rogue that loves his sword so much it has become magical to him. If anyone has any suggestions please let me know!

Notes: This is my first post on GITP, and if I did not do anything correctly please inform me. I hope to continue using these forums, as I've seen that most people around here seem to be both nice and knowledgeable.

Link to Stone Sorcery: can't link, not enough posts by me

[Easy_Lee]

Proficiencies gained from an archetype can be picked up via multiclassing - part of the reason why Life Cleric is a popular dip. You can use a shield and still Booming Blade. Searing Smite and any other smite that says "the next attack" or "when you hit with an attack" will work with Booming Blade.

The build is practical. If you intend to use a shield, I would strongly consider Warcaster.

[Abenadia]

Thank you very much! I might consider that as a feat, but I believe that only the opportunity attack portion will be relevant. I plan to only dip very lightly into sorcerer, so I don’t believe I will have any relevant spells with somatic components. I also plan on using only concentration spells that end quickly or immediately, so advantage on saves to keep concentrating probably won’t be too helpful. Thanks again though, I’m glad to know I’m understanding all the rules correctly. I’m pretty new to D&D, and it’s been great so far.

[Easy_Lee]

Thank you very much! I might consider that as a feat, but I believe that only the opportunity attack portion will be relevant. I plan to only dip very lightly into sorcerer, so I don’t believe I will have any relevant spells with somatic components. I also plan on using only concentration spells that end quickly or immediately, so advantage on saves to keep concentrating probably won’t be too helpful. Thanks again though, I’m glad to know I’m understanding all the rules correctly. I’m pretty new to D&D, and it’s been great so far.

If only going for a small dip, would you consider Magic Initiate and Moderately Armored instead? The former will get you the cantrip and one spell once a day, and the latter is a half feat and easy to work into an odd attribute. That path is a bit more common for rogues who aren't Arcane Tricksters and want to use Booming Blade.

[Abenadia]

If only going for a small dip, would you consider Magic Initiate and Moderately Armored instead? The former will get you the cantrip and one spell once a day, and the latter is a half feat and easy to work into an odd attribute. That path is a bit more common for rogues who aren't Arcane Tricksters and want to use Booming Blade.

I did consider this, but it would mean that it would require a level 8 or above character. We are playing at level 4, which would mean I would need to choose between spell attacks and shields, having only one for 4 more levels. Medium armor would also not be a huge boon to me because I will increase my dexterity to 18 by level 5 (Kenku race), where a +4 bonus will mean much more to me in terms of AC than +2 from dex and +other from armor. I think the access to 4 cantrips and 2 level 1 spells (I am going for Thunderous and Searing smite) immediately, as well as more spell slots if I decide to take another sorcerer level, will make this a more versatile character early on. If UA were not allowed, then the aforementioned path would be the best choice for me.