if you currently run 8.5 x 18's with no problem then your hardly going to have any issues with another set of wheels of the same size, unless you were to go for a drastically different offset.

order them from Martoon, thats why he had the 8.5" commisioned - to suit the escort cossie's and he will ensure you have the correct offset to suit your application.

on mine i run 9 x 18 comp's with 245/35/18 and have no arch issues so im sure you will be fine.

depends on what style of comp you want to go for, as to which you preffer the look of.
the 8" and the 8.5" have almost flush spokes to the edge of the rim, where as the 9" have a slightly deep rim/lip to them.

HTH.