Specific questions about the expat status in Belgium

Dear all,

I would like to seek a bit of clarity about one of the points regarding the expat status in Belgium. And then clarity about a couple of more issues strictly related to it.
The point is this: "Non-recurring expenses (moving costs, installation costs) are not subject to Belgian income tax without any ceiling (if conditions are fulfilled). Recurring allowances or expenses paid during the employment in Belgium (cost of living differential between Belgium and the home country, housing differential, the difference in income taxes, the annual home leave, etc…) are in principle tax free subject to an annual ceiling of EUR 11.250 or EUR 29.750. The higher ceiling of EUR 29.750 is applicable for
activities of a controlling or coordinating nature or for scientific research."

1) About the moving costs: assume I will spend 10000 euros to move to Belgium: then, will I have to report those 10000 euros within my tax statement so that they will not be taxed?

2) How do I quantify/calculate the cost of living differential and house differential between home country and Belgium? And then again, shall I report those values to my tax declaration?

3) My possible future employer wrote to me something mysterious: "If [my employer] does not intervene in these moving expenses and the employee pays them himself, it will not be advantageous for the expatriate to deduct these expenses as a professional cost in his tax return as he would lose the advantage of the forfaitary professional costs to which he is entitled to".
Knowing that my employer will not pay for my move, what is the "the advantage of the forfaitary professional costs to which he is entitled to" am I going to lose? I had asked the employer, without receiving any answer. I have never read of such forfaitary professional costs the company is referring to.

4) My employer will not specify in the contract I would sign, that I am going to get the expat status, though they say they will help me with this. Is it common practice instead to specify such thing?

5) The employer (a research institution) is putting quite a lot of pressure so that I sign, without providing me the amount of information I keep requesting with no avail. I am feeling a bit uneasy in this respect. I am feeling that after I will have signed, they will not support my status, or they will not help me. In any case, the point is this: if one signs a contract, and then decides not to start to work anymore for that company: can he give notice to the employer? My start date would be in a few (five) months from now. Could I sign, then (if I realize the employer wants to screw me) give notice and never start to work? If I do so, are they entitled to any sort of reimbursement from my end? I do not yet live in Belgium by the way, should they want to sue me.

Thanks