1. Front brake only is standard on fixed gear bikes, since your legs can apply stopping force to the rear wheel. You could leave the rear brake on for awhile and try it both ways.
2. Are you talking about chain alignment on 700c vs 27"? Chain alignment would be a function of the hub, not the rim size. If the bike has 27" wheels now, you know that the brakes have the right reach for that size rim. If you switched to 700c you'd have to check frame clearance and brake reach.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72