Help with building out a samurai(ya I know there are better subclasses) fighter with 2024 rules

I was wondering if I could get help building out my Geppetin (living plush) Samurai fighter at lvl 4 my scores are str 16 dex 12 con 16 int 8 wis 14 cha 11… went with the Harper agent background for character backstory reasons and am currently wielding a long sword and wearing splint armor we just lvled to 4 so was gonna switch my fighting style and also didn’t know if I should up my strength to a 18 or take a feat(was debating between slasher or sentinel)suggestions would be good… was wondering if I could get suggestions on how to build him out to lvl 13…. Mostly gonna stay melee and probably stick to long swords but I know as a fighter you are master of many weapons… also should I multiclass and if so what ones and how many lvls

What’s your role in the party? Sword and board usually says tanking. Beyond that, what are you looking to do? It’s tough to help you make your character without knowing what you’re doing. 
With samurai, it’s pretty generic and easy to bend in any direction. Just remember to use your fighting spirit before you action surge.

As far as multiclassing, your options are cleric and Druid. A couple levels of cleric might be useful, but it will depend on what you’re trying to pull off. That said, I would not likely recommend it. You might get a few buff spells, but your hands will be full, so casting them is going to be a pain.

Sorry for the late response… was planning to be more tanky currently have the highest party AC currently welding my long sword two handed but might go back to sword and board to get more AC…. But I kinda was wondering if there was some options I could take through lvling up that would make me more tacticy(if that makes sense)

If you’re trying to be tanky, definitely get a shield. While you can use a longsword with 2 hands, if you’re going to use 2 hands, you’re much better off using a heavy weapon and getting the perks that come with it.

Sword and single weapon does give you lots of options.with the 24 rules, you should consider masteries. Longsword has sap, and handing out disadvantage is really good for a tank. You might also consider a warhammer, as push can be very helpful as well, since you can knock enemies away from your allies.

Sentinel is a great feat for being a tank, really a must have if you’re trying to lock down enemies. Slasher isn’t bad in theory. But the slow effect I find doesn’t come up often. For one, once you’re in melee, most enemies aren’t going to try to move, so slowing them doesn’t help much. For two, if you already have sentinel, you just going to stop them cold, so being slowed won’t matter much.

Other things to consider could be just boosting str. You want to be a threat, and a high str will help you hit more and be more threatening. And boosting con, if you’re the tank, you want more hp. 
The Harper Teamwork fest could be interesting. A samurai could get done benefit from the cha boost. You’ll never use the help action in combat, but ending frightened or paralyzed on an ally could end up being useful (with indomitable you should be able to make your save). But that will be campaign dependent, since maybe those conditions won’t come up much.

I really wouldn’t multiclass. My first through was spirit guardians would be good on a tank, but that would mean 5 levels of cleric, which is a really big investment. And with your wis score, your save DC would be pretty low.

You said you’re thinking about changing fighting style. What is it now? I’d suggest defense (as a tank, higher ac is good) or dueling if you add that shield (extra damage to make up for going 1-handed and more damage makes you more of a threat enemies can’t ignore.)