The word "God" would not have bothered the founding fathers, it's a generic term that in no way claims any particular Religion is right or wrong.
Yes indeed. But you could certainly not say the same for those who modified the pledge in 1954.
The declaration was written by Jefferson, whose religious views deserve their own wikipedia page and are hard to summarise.
While Jefferson uses the word God, it is far from the same sense used by the conservative Christians of 1954.
Politically, they were the antithesis of Jefferson. Interestingly, the original pledge was written by a Christian socialist, but made no mention of religion.
And I really cannot see Jefferson putting God into any pledge.