I received a Note 4 and am attempting to upgrade the OS to Oreo. However, it does not have a SIM card yet as I will swap mine in after the upgrade. Is it possible to root/unlock the bootloader without a SIM card?
Yes it's possible to root. It's possible to unlock the bootloader on some variants, impossible on others. With or without a SIM card in both cases.
And I don't think there's an Oreo out for the Note 4. It came out with 4.4.4, so with 2 upgrades, it should go to Marshmallow. If you want to upgrade it to Oreo, if you have the 910F, G, P, R4, T, T3, V, W8, 9100ZC, ZH, 6W, 9W, you can upgrade to LineageOS 15.1 at https://forum.xda-developers.com/no...eo-8-1-0-unofficial-lineage-15-1-rom-t3760969 If you have other variants (like the 910A), you'd have to write the modifications yourself.