You've already gotten many good replies and important perspectives concerning schools and places to live around Zug. I have no experience with local Swiss school, but have three small children who attended ISZL since preschool and onwards.
We have had only good experiences with ISZL. Preschool (children from 3 yr) has been amazing and truly developed our daugther, socially as academically (our other two children first started at ISZL from prekindergarten). I was impressed with how they used play on academic matters as letters, numbers and shapes in experiments (e.g. physics, biology), gardening and small explorer trips into the woods, supermarket, kitchen (cooking/baking) etc.
We are not native English speakers. This means while native/advanced English speaking children are having German lessons, our 6 year old child together with others is receiving extra English lessons (this started last year while she was 5 years old). It is a win-win, the native English speaking children get challenged in getting better at German while our children improve their English skills.
Still, our children receive German lessons at school too, they are just learning it at a slower speed. It is their third language and they are still quite young (4, 6 and 9 years old). We'll get there
We all practise German at home as well where we speak German with our lovely Swiss neighbours.
I have heard good things about the local schools too, however to me personally, it would be a stressful issue with the lunch break where I would have to be home, have lunch prepared every day from 12-13 and after that one or two of the children would have to return to school for maybe an hour only. To me it seems like a lot of coming and going on a daily basis where I would be stuck to the house preparing lunch and looking after children.
It suits our routines well that the children are all together at one place at the same time, from 8.50- 15.30. The activities in school are made suitable for the childrens age, meaning that the little ones have more breaks and 'quiet time' as well.
For us ISZL has been a good solution. Now this year our children have started attending some of the free club activities after school and they have made many good friends at the school
It is of course a personal choice what is best for you and your family. In our case the company pays most school fees and we didn't know on arrival how long time we were to stay in CH. We came from an English speaking country and felt that it would best for our children to continue the 'red thread' in school with English being the tuition language.
If you already now know you will be on a local/long term contract the local school may be a better choice for you as it often makes a great short cut to get to know locals (children as well as grown ups) at a much faster speed (from what I heard).
Good luck and welcome to Zug. I hope you will all be happy here