Is this suitable for a .....?

We are going to be looking after our cousin's dog whilst they're away on holiday. We know what he eats and his walks etc etc everything to the vet's name and the receptionist! Only thing we aren't sure of is: Its a puppy so has a medium cage (a large puppy lol) The cage is in the kitchen which during the day time is really bright and warm as the back gets all the sun, during the night time, very very dark apart from a light glow from the street light. If we pull the roller blinds down at night and shut the curtains will it create a happier place for sleep, or at least help him to sleep, and during the day, would it be best if we kept things open for him (blinds not windows lol)? Also, the cage has a mattress with a fluffy sheepskin part at the top, a blanket on top so its cosy and then a little fleece the breeders gave my sister when they bough the puppy so it has the siblings scent. There's a thin blue blanket dd over the entire cage too so its more 'den' like. Is this alright, as its summer it may be too hot for him, or will it be cosy enough. We're getting our own dog soon and thinking of the same arrangement, but we're getting a Sheltie.....so very long hair suring the summer and blankets may be too much?? Thanks in advance.