You can remove the sump while the engine is still in the car if you only want to change the big end bearings, to change the mains you would be best to take the engine out, you will have to raise the engine on the drivers side a fair amount (best to release the exhaust down pipe and dog bone engine mount as well) so you have room to manouver the sump down and miss the oil pump there are a few of the sump torques bolts which are a right pain to get at. Oil pressure hot should be between .5 and 1 bar at idle and between 2.5 to 3 bar at 3000rpm.