"Re the leaving the pup by itself, have you considered getting two puppies?! Not that much more work than one and they'll be company for each other."
Two puppies are far more work than one, and often fight as they mature, leading to behavioural problems and resultant rehoming.
"We have a big garden, so we can shut her out of the house when we are not there, she is at a naughty phase so she is now tied up outside (with access to shelter, food and water) when we are not here."
I consider this to utterly inappropriate for a (young) any dog's needs, for all the reasons so far mentioned by other posters, and more. Where's Valhalla when you need her??
"We have a puppy who is 7months and 2 boys, 3&4 and I don't work so I'm home with her all day. It's not just leaving the puppy when ur working, what about the other times your out, doing shopping, visiting freinds, it's very restricting! I love her and the boys thinks she's great, but given my time again, I wouldn't do it. Plus they really Do chew everything, especially when bored, and she has destroyed our once lovely garden! And we have another 15 years of it!"
Excellent experiential advice - please take heed of this OP.
OP you seem to have given this some consideration, and if you're able and willing to employ a dog walker to break up the monotony of the days when you're at work, then that's good. Where's Valhalla's advice when you need it? [grin}