Without being there it's hard to know if the attachment is adequate. Large washers under the screws might help.

Having just recently begun flying off floats I can say it is quite easy but even if it's calm and things are done right the floats still take some beating. Water does provide some resistance even if you just touch it initally on landing. I was surprised though at how relaxing it can be when you have a LARGE runway and no trees to avoid on final.

The step, up to 1 inch behind the CG, is OK but the 1/4 inch mentioned is probably ideal. I know I stirred up a little water on my initial run ups and having the step more forward would have eliminated some of it.

You still have to keep the CG in the right region relative to leading edge of the wing, so that has to be checked. It changed- you put floats on.