Sorcadin

GWM is a mighty tool in the hands of anyone that can work with it, and the sorcadin's a good fit for it. The loss of +2 AC can hurt, but you also don't need war caster, ever. Variant human is advisable so you can pump your strength at level 4, but it's by no means a crime to go half-elf or something similar and grab GWM on your first ASI.

Normally I advise going into sorcerer at your third level, but if I were planning on taking GWM, I'd probably not make the switch until after I got six full levels in paladin. More than other sorcadins, you need extra attack ASAP. You're also really in need of strength more than usual, because you need the accuracy boost to make GWM more reliable. This isn't that big of a deal, of course- paladin is a perfectly strong class all by itself. You could also make the hop to sorcerer after 5 levels instead of 6, I'd just be jonesing for aura of protection at that point.

You'll also have the superior paladin hit dice, and if you're really fearful of getting hurt, the defense fighting style puts you at only a -1 AC compared to S&B. I'd probably go this route anyway, unless the DM wants to house rule using great weapon fighting style rerolls on smite dice. If they rule that way, which is weirdly a common house rule, then take it and don't look back. Your smites will be the smites of the gods. Doesn't hurt to ask.

Your charisma will suffer until late game, be mindful of this. If going variant human, you'll cap strength at level 10 and then not get a chance to increase charisma until level 14, which is fairly late. You won't cap until level 18, or at all if you take another feat of any sort. If going anything but variant human, you will simply never cap charisma, ending at an 18-. Which isn't bad at all, mind you. Still, before you can boost your charisma in either case, I'd advise not picking up too many spells that require attack rolls or enemy saving throws, as you'll fail at them against anything with competent saves. Either make sure to target things with saves they can't easily make (dex versus dragons and giants, wis versus ogres, constitution versus casters, etc.), or focus on buffs and support spells. You certainly have enough good ones to make it work.

Now for damage tables. At level 1, assuming variant human for the feat, you'll be doing 20 damage any time you hit with it, which will be ~40% of the time versus enemies at that level. Despite the low accuracy... I would always do this. In a heartbeat. Your damage without GWM is only 25% more accurate for exactly half the damage, at 10. Math says GWM and put on your troll face. You're essentially threatening to end any combatant in a single swing every time you do it. The damage is so high that you will kill all pre-CR 2 enemies in a single hit, which is most everything but bosses before level 3. You're going to be 2-3 shotting CR 2 and 3, the erstwhile bosses during these levels.

Later, assuming a level 11 GWM pal 6/sorc 5, you'll have two attacks followed by access to a third via quickened GFB or BB, or even just a GWM proc (GFB and BB do more damage, but always take the proc if you get it. No resource expenditure trumps the extra damage). If using GWM, which should always be turned on unless your opponent is in particularly heavy armor (there's a table out there somewhere to explain when it works best, but general rule is- don't use it against anything in heavy armor and carrying a shield until your attack bonus gets to around +10), you're likely to miss one of these attacks every turn. This is perfectly acceptable, because you hit for 2d6+15, or 22, per regular attack. GFB will add 9 average extra damage for 31 when that's what hits. Disregarding that and saying you essentially only got two normal attacks off, that's 44 damage a turn with mild resource expenditure.

When you add in 22.5 (5d8) extra from your best smites, you're talking 66+ damage rounds, on average, with no buffs running. Greater invisibility is a good trick on a normal sorcadin, but it's monstrous on you- all three attacks are likely to hit all but the most heavily armored targets, and assuming the GFB, we're now at 75 damage per turn before you do any smiting, all for a level 3 concentration spell and a single spell point each round. While you can't keep that up indefinitely, you can reliably do this three times a day, running ten rounds each time you do (essentially one entire fight, anything that goes past 10 rounds of combat has gone very south already). And on top of this, anything trying to hit you will probably have disadvantage thanks to being, ya know, invisible. Assuming they even know where you are.

There are other tricks as well, including quickened hold person (which, if successful, will hand you the fight on a silver platter), quickened fireball before charging in to soften up some targets before the smiting begins, haste which is nearly as good as greater invisibility for damage (and occasionally better if you can get advantage from something else or were unlikely to miss in the first place), or if you feel like trolling, booming blade followed by a quickened shocking grasp before casually walking away.

Tl;dr: It's perfectly viable and the damage is good from even level 1, but I wouldn't branch out into sorcerer levels until later, and I'd focus on capping strength before touching charisma. Abuse GWM like it's going out of style.