Hi Izabela, don't be put off from your first tender, we all have to start somewhere and your moving in the right direction by seeking help.
I have completed many tenders in my time with some success
First off, if the tender is posted on the European Journal its likely to exceed £50K per annum, if its published you can expect between 20 and 50 suppliers to register interest, ranging from large nationals to local and regional providers. If it's a closed list there will be fewer responses and I would be keen to know if you were invited, or are replying to an advertised opportunity. Most Schools use a Tender Firm who have a set format for their tenders, having completed your first tender response most of the detail can be used for subsequent responses from the same author.
Regarding Qualification, have you completed a "Pre Qualification Questionnaire" and have you qualified the opportunity before you include the costs to reply.
The Tender Notification will normally say a price range, my experience is that the Tender document will include a "Preliminary Contract" and most bodies are not very flexible to change their contracts so read through the requirements and your commitments carefully to divide if the contract is appropriate.
As a guide, if the contract value is in excess of 20% of your turnover you may not qualify by the awarding authority, if the contract value exceeds 10% of your turnover you may struggle to manage your other contracts.
Assuming you have already completed and documented your policies, I would suggest circa 4/5 man days to complete a professional response to a tender, to include your value, missions and how you will continually deliver, and improve the service at a competitive cost.
Sorry to drone on and I hope that some of the information here is helpful
Kind regards
GeoffDerby