Upgrade my MacBook storage, move all the software on my MacBook to a hard drive

sorry, but on M.x Macs, you cannot upgrade the storage after the fact.

but if you need extra storage, you absolutely can use an external HDD (or more than one) and save data on it. there are several ways to move your data to an external drive. one way is to open two finder windows, one for the external HDD, and one for your local drive. then it's just a matter of "drag and drop" to move files to the external drive. once they are on the external drive, you can remove them from your local drive.

but when it comes to the external drive, please do not use any of the manufacturer's software on it that supposedly makes the drive "Mac ready". when you use software from just about any manufacturer for their storage device you run the risk of that same software not being compatible with macOS updates / upgrades. it can cause the software to stop working. at best this will cause you a headache. at worst it can render your data inaccessible. it is always best to use disk utility to erase and format a drive before use to remove any preloaded software.

please see Erase and reformat a storage device in Disk Utility on Mac - Apple Support.

also, it's a good idea to keep ~20% of your local drive as free space. FWIW, I personally keep very little on my local drive.

Just as jefferythefrog says, you can freely use an external drive.

BUT: but what needs to go on it is your files, NOT Applications.

Applications need to remain in the /Applications folder, where they are protected as part of the crypto-locked System Volume, and if you move some to another drive they will also not be able to execute as quickly.