Hi Steve I have a TA357 and this is what the manual recommends for the glow plugs: 0 to -5, 10 seconds, -5 to -10, 10 to 20 seconds, -10 to -20, 20 to 30 seconds, -20 or more, 30 seconds or as required (these are all celcius by the way). My tractor does not have the eye with the coil that glows. If yours does you should use that as your guide for how long to preheat being careful not to hold it on longer than you need to since you can burn them out if they're held on too long. Set your throttle at half and once coil glows bright red start the tractor. As soon as it starts back the throttle off a bit. If it doesn't start readily like that you may have glowplug issues.
As to the proper oil to use in your front axle good quality 80-90W gear oil is what you want for that. Gerry