If you are going to do a Belly up then I would do the SYE/DS at the same time. Figure that the belly up will probably move the TCase somewhere around 2.5 to 3" so you are going to effectively change your pinion angle. So those two mods are very suited to do at the same time.
For an oil pan skid to work with whichever belly up will be determined on which ones you go with or how much you can modify it to fit. Some of the different manufacturer's make skid to go with their belly pan setups.
And no, with the belly up skids that are on the market today you shouldn't need anything other than your a 1" or 1.25" BL to fit them. (Since Nth stopped making their completely flat skid)
For an oil pan skid to work with whichever belly up will be determined on which ones you go with or how much you can modify it to fit. Some of the different manufacturer's make skid to go with their belly pan setups.
And no, with the belly up skids that are on the market today you shouldn't need anything other than your a 1" or 1.25" BL to fit them. (Since Nth stopped making their completely flat skid)