Before you put the caliper and pads back on you'll have to push the piston back into the caliper to make way for a wider disc and pads.
I normally use a G clamp to push the piston back into the caliper, you can lever them in too but be careful that you don't damage the piston seals.
Check the sliders on the J spec caliper to make sure they're okay.
Your brake fluid reservoir level will go up aswell so unscrew the cap and make sure it doesn''t overflow, you may have to remove some.
You can leave the flexible hose connected but obviously the caliper will still remain attached to the car by the hose, just make sure you don't damage the hose at all.