
Karen,
I took my Rough Collie pup on holiday at 4 months, along with her mother, plus two friends and their adult dogs. (What a carful that was!) Didn't have any major issue, just had to make sure I kept the exercise at a sensible level as it's easy to get carried away and let them overdo it.
I would NOT have considered doing this without having a crate to keep her in whilst not being watched 100% percent, as I feel very strongly that if we do not respect rental cottages with our dogs, in a very short time owners will get tired of this and will not allow dog owners to use them. Need to bear this in mind in the garden as well, obviously! In fact, any dogs I take to rental cottages always sleep overnight in crates - although I do not use them this way at home, I make sure the dogs are happy with it before I go away.
However, points to think of would be that I went early in the year, and you are looking at high summer - your pup will be too young to be on the go all day, and it is likely to be too hot to leave him/her in the car. This will limit you. Also, we had the use of a fantastic beach, which thankfully is open to dogs - don't know where you are, but we stayed in Carhampton, 5 minutes drive from Blue Anchor Bay - but this is also often limited at high season.
That said, we all had a great time, and have some lovely photos to remind us!
Marina