Spacers are safe, but you really should get hubcentric ones as mentioned, this means that the spacer uses the exact pcd and centre bore size as your original hub so the spacers fit on tight to the hub. Cheap spacers have several holes for a universal fitment of all different pcd's and will have a huge centre bore hole which means they have a load of movement on the hub when you fit them.
So, you want to get some 10mm 5x112 57.1 centre bore hubcentric spacers, and a full set of longer wheel bolts to be on the safe side, I'm sure you can use the original bolts on 10mm spacers but to be honest I'd rather be safe than sorry, you would be loosing 10mm of thread on your original bolts if you didn't change them at the end of the day.
The 255 tyres are definately too wide if your going to be running spacers on a 9" wide wheel, 235's would be perfect, whilst 225's would give quite a bit of stretch on the side wall, which is fine if that's the look your after.