Depends on your distance. If you bike 10km say, downhill most of the time, you can make do with suits.
You shouldn't be getting bike grime into your pants unless you live in a rural area though.... or a really dirty street.

For most lubes, it's sufficient to have 1 drop of lube every 3 links or so. 1 drop every 3 tooth or so on the front derailuer, and 1 drop every 5 tooth or so on the back wheel. MAKE SURE TO WIPE OFF EXCESS LUBE. You only raelly need lube inside the chain, not thickly coating the outside of it. Take a old cotton shirt and put some gentle pressure on the chain and run it through a couple times. If you wiped too much off, you can put some more in. The more lube there is, the more dirt it attracts.

As for clothes, I change. There's a YMCA near my work, and I'm a member there, so that saves me some grief. I can use their lockers there as well for the day. I have ridden without changing, though. Take some kleenex or paper towels to wipe off hands, face, neck, and armpits. Makes sense to bring some deodorant and some sport-type cologne to mask smell of sweat if you're that worried. Most people swear more on their torso then their lower body, so just go to work in a nice t-shirt and change your shirt at work!