You will still have to do a bit of running in a cyclo cross race. If it is racing you are interested in then cyclo cross is a good workout. One hour of maxing your heart rate in winter. If you aren't really a racer then a cyclo cross I think would be a bit restricting. If you are interested in keeping fit then a mountain bike would offer you more fun in the mud.

I'm assuming you want to race cyclo cross in which case most racers use clipless mtb pedals and shoes which have the cleats in a recess in the shoe so you can run/walk in them when off the bike. As for the bike the Giant is a very good expert level cross bike but there are cheaper alternatives out there if you just want to test the water.

Make sure you get a pair with threaded holes for fitting studs so you have that option. If you go for mtb instead of cyclocross then you can cut out the running altogether!   If you have a knee problem then a lot of folks say that Time pedals are easier on the knees than Shimanos, cos they have more 'float' (freedom to twist the foot whilst clipped in). If I wasn't already very happy with Shimano M540s then I reckon Time XE's would certainly be worth a look. Be prepared to experiment with the cleat position to find your most comfortable setup.

PS. Get into Mountain Biking - the bikes are more comfy than cyclocross bikes.