What percentage of a type 1 diabetic father's children will be type 1 diabetics also?

Low. In the past I have read the risk is at or less than 5% in any offspring of a type one.The risk of type 2 would be a separate issue and relate to the risk in the general population. You will be aware and more vigilant to the symptoms than most, and I would not make this a reason to avoid parenthood.
Difficult to say. Type 1 diabetes is caused by several genes and there must also be an environmental factor that we don't fully understand. We know this because in identical twins (therefore same genes) one can develop type1 while the other does not.