You'll need the tool as its virtually impossible to turn the pistons without it, i managed to remove and re-use my abs rings although i could easily see how they could get damaged during removal also take the discs and bearings to a garage and get them to press the bearings in for you as the idea about bashing them in with a suitable sized socket is total crap...they need pressing in properly.
The caliper is removed by undoing the two allen head slide bolts..one on top...one on the bottom, then you'll need to remove the caliper carrier bolts behind the disc..these are also allen head bolts and will be a swine to remove, buy a proper allen key socket to fit (8mm).. i bought a teng one off ebay for about six quid and have a set of irwin extractors ready for when the allen bolt rounds off which it will.