Typical lease is 3 years minimum but we managed to negotiate 2 years, you could try to negotiate less if you wanted to (we tried initially but the agency spoke to us like we were aliens).
The really key thing is that normally there is no breakage clause ie you have to complete that minimum period, and - very important - it is then renewed for a full year at a time, again with no breakage clause. Even to stop the renewal happening, you have to give 3 months' notice, and once it is renewed you are bound until the yearly renewal date. You may be able to get out of it if you find tenants the landlord deems suitable.
What we did was to agree on a 2-year minimum and then insist on a clause which said that after that 2 years we could give 3 months notice at any time. We explained that we would only be wanting to move in order to buy a house...
You should also include a 'diplomatic clause' which says that if your husband has to move for his job (unlikely with the EU but it's possible he may not like it, and of course things are a bit unstable right now) you can break the contract.
Not sure about the IT field though I would imagine there would be jobs in that area even without French or German - try to do some research.
For the schools, in theory there is no difference, the curriculum is the same for all European schools. Bear in mind though that there are difficulties in the English section as they struggle to recruit native-speaker teachers, and the impact of Brexit is very unclear.
The Mamer school is only a few years old and has very nice sports facilities, but I think either school would be fine. The advantage of Kirchberg is that your child may be very near your husband's workplace (if he's in Kirchberg) which makes things easier for picking up a sick child, attending school events etc.
Personally I would look more at where you want to live in terms of commuting, cost, managing school runs (possibly including school bus routes for later) etc.
Also, look at the enrolment policy: www.euroschool.lu/esluxone/Documents/Home/Enrolment/Application/Policy/2017-2018/2017-2018_Admissions_Policy_approved.pdf
- it says that new residents (ie who are not resident in Lux at the time of making the application) are automatically enrolled in the Mamer school.
Good luck!