Backing up from old computer

When you connect your TM drive to the new machine it will ask you if you want to transfer so yes all will be transferred. Just remember that any old 32bit apps (if you had any on an older OS) will not longer work with the new OS.

Transfer to a new Mac with Migration Assistant - Apple Support

When you buy a new Mac the easiest, quickest and most reliable method to migrate from the old Mac to the new Mac is to simply connect the old Mac's Time Machine External Hard Disk to the new Mac using a USB cable before you turn on the new Mac. You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less. When you start the new Mac for the first time it will startup Setup Assistant (SA), SA will get to a point where it asks if you are migrating from another computer, select Yes  and follow the on-screen prompts and it's done! It is THAT simple. Migrations are an all or nothing, you cannot select which files you want to migrate. For most the best solution is the migrate everything then remove the data you do not want from the new machine.

If you have already done SA on the new computer then simply connect the Time Machine External Hard Disk using a USB cable and launch Migration Assistant (MA) which is located in Applications - Utilities - MA. Then follow the on-screen prompts. 

The ONLY difference between MA and SA is MA will create a new user account that you need to log into.

Both SA and MA migrate applications (not 32 bit apps), data files & settings. They do not migrate Mac OS itself. Some professional apps such as Adobe and Microsoft apps may require re-installing their apps as they will not allow them to be migrated. As long as you kept the security keys for installing their apps, it is not an issue. 

Finally, never EVER use Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in most cases. Please read and follow the directions in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup of the older Mac then create one! If you are not aware of Time Machine, please read Back up your Mac with Time Machine and finally if you need an External Hard Disk to use as a Time Machine External Hard Disk then many experience users on these forums prefer the OWC Mercury Elite Pro due to it's reasonable price, high level of quality and ease of use. 

If they are in iCloud there is no need to copy them as they are already there. Once you setup the new computer using Setup Assistant and sign-in using the same AppleID as you have on the old computer all your iCloud stuff is there. If you are going to use migrate, then just migrate your settings and do not migrate your data. You can migrate:

• Settings
• Apps
• Data

However when you select one of the above it is all or nothing. For example if you select Data, it will migrate all of your data. If you select Apps it will migrate all of your 64bit apps, very old 32bit apps will not migrate!

Before you migrate the old Mac download and run the free GO64 app to find out which apps will not work so you can remove them before migrating. I use AppCleaner to remove the apps and all supporting files which many have installed in numerous places. Just be sure to heed the warning below.

WARNING: If you use AppCleaner on an app that you have other apps from the same developer, like Adobe, you must be extremely careful checking all checkboxes and deleting.  Some for those files may support other apps from the same developer and deleting them can mess them up.  Adobe apps is a primary example. I know from experience.  For singular apps from a developer it's safe.

After removing the 32 bit apps you can make a final Time Machine backup and start the migration.

You can only pick categories but you can always delete old apps after the fact.

Yes it will work fine as long as the old computer is running an earlier version of Mac OS than the new computer.