Definetely have air blowing into the case - especially if your heatercore is mounted in the bottom front of the case, where exhausting does nothing beneficial due to the positioning (hot air rises). If you do a ceiling mount it's a different story - but the cooler air is outside the case, and you want the coolest air you can get going through the radiator.
For mounting - I find that with steel the easiest way to cut your fan hole is with a jigsaw, or a Hole saw, afetr carefully scribing the hole you need to cut. I do all my cutting at my school, where we have an extensive shop room, and I have tons of tools at my disposal - If you don't have access to such things (I bought my 120mm, and 80mm hole saws online, and they were extremely inexpensive - PM me if you want a link) then investing in a dremel tool, a decent hand drill, and a few hole saws is worth your money.
For the shroud mounts it is a good idea to use washers, and self tapping screws (or get a tap, and tap your own threads) - the Chieftec case has honeycombed grills in the front, which you will be chopping through when you cut your fan hole, and I found washers to be neccessary for a solid mount.
I also use bicycle inner tubing underneath the radiator, and between the case contact. It kills vibration, and provides a soft 'bed' for the radiator to rest on, nice if you're lugging your case around for whatever reason.