I plan on taking the Magic Initiate feat with a paladin, giving him light, fire bolt, and shield from the sorcerer list. For light and fire bolt I can sheathe my sword as a free object interaction on my turn, then cast with my free hand, and redraw sword on my next turn to continue stabbing baddies; the same is true with all my other somatic spells. But since shield is a reaction, I assume that means I won't have time to sheathe my sword and do the somatic aspect of the spell in time?
Technically, could I get around it by always sheathing my sword every round that I'm expecting to take a big hit?
I want to RP that these are additional spells I've been gifted by Bahamut or a powerful dragon (I'm dragonborn), since they all make sense as holy abilities. Probably best to talk to my DM and see if they'll just let me use it without having to say "I sheathe my sword" "I draw my sword" 100 times? Plus it is only once a day, so not crazy OP.
Best Answer
It's Possible, But Tricky
You've correctly identified the difficulty of "sword and board" characters casting Shield. Shield is a great example of a spell that justifies the distinction between somatic and material components: it's a spell that is easy for non-shield wielding squishy spellcasters to cast, but difficult for the heavily armored heavy hitters (even those that can use a shield or weapon as a spell focus).
You could try dropping your sword at the end of every turn (this wouldn't cost any kind of action, as JC has clarified in tweets) and then be able to cast Shield as a reaction, and pick up your sword at the start of your turn. But this risks the possibility that an enemy could pick up your sword during their turn (either attacking you with it, or running away with it, or throwing it off a cliff etc.). That'd also stop you from making Opportunity Attacks with your sword (which also take your Reaction, but might come up on different turns than the need to use Shield).
The safest option is to get the Warcaster Feat, which would also give you advantage on Concentration Saving Throws.