For the loctite on the bolt threads, make it one drop of blue. Factory puts a lot of loctite on some bolts, and they are often hell to remove(rear drive shaft bolts). The red loctite is for super strong and tight bolts, do not use that. The blue is a mild strength, great for most all small bolts, but one drop is enough.
If the rear needs cleaning, you should do that before installing any parts. Do it after pulling the axles, use old rags etc, as needed, to push through to wipe the inner housing etc. Engine degreaser is helpful sometimes also for nasty grease that brake cleaner would need more of. Always finish with a brake cleaner product type, it evaporates and leaves the least residue behind. It doesn't have to be spotless, you just want all the loose metallic particles out, those will damage bearings.
You don't need to pack the axle seals, the bearings and seals do need a little oil(diff grease) on them, a finger applied amount is good. If you don;t touch the axle seals with the axle when putting them in, the seals will not be hurt. Once you get past the seal and through the bearing, the seals aren't any problem then. Just feed the axle into the diff, do the c-clips etc.
That center pin though, that should not need to be forced in. With everything cleaned, then test fit the pin, without forcing it. See if anything is impeding it's movement into place. If there's a burr or something that can be removed(filed smooth etc), do that before putting a little grease on it and pushing it in.