I Love the Bucas serie. You Can buy A lot What fits your hore and his situation.
Well Connemaras are pretty hardy so I'd say if your stable is nice and warm then he won't need a stable rug. But if it's one that can get cold he might just cause he'll be used to being rugged. Cause once they're rugged they'll find it a bit harder to warm themselves naturally. As for the outdoor one if it's just to keep rain off then you won't need a heavy one and I'd say the 50g should suit fine!
The rug is more to keep the rain off him tho. He's a Connemara. Would he need it on inside if he only has a 50g fill
I'm also Irish so I feel your pain! It really depends on your horse and your preference! The thicker the denier the thicker the rug... if you have a lighter horse like a tb they might need a heavier one than a cob or if your horse particularly feels the cold? I'd recommend an indoor rug for stabling and hang the outdoor one up at night then to let it dry.
Depends on thick hair your horse have and what temperature you have in ireland at the moment.
If i were you i would have a lightweight rainblanket outside and thicker when the horse is in the stable. Never let the horse stand with a cold and wet blanket.