using cloud as well as an external hard drive

If these are new images that are still on the card, then when you import them to LrC using the import dialog simply choose a destination folder on the external hard drive. If the images are already on your internal hard drive, and haven't been imported to Lightroom yet, I would use your system browser and copy them to the external hard drive first and then import them to Lightroom.

Remember that since you are using Lightroom Classic, even though you synchronize to the cloud when you have fast Internet you aren't going to send the full-sized images to the cloud. Lightroom Classic only has the capability to send smart previews. The full-sized images remain on your computer hard drive or external hard drive. If it is imperative that you must have full-sized images in the cloud then you should consider Lightroom 3.4. It is a completely different Lightroom, has different features, works on a completely different philosophy. I don't believe it is what you would want in your situation, but it is the only version of Lightroom that will enable you to have full-sized images in the cloud.

If you are using Lightroom Classic then you really don't need 1 TB of cloud storage because all LrC sends to the cloud is smart previews, and they don't impact your cloud storage at all. You cannot put full-sized images in the cloud from LrC.

If you are using the Sync feature in LrC to Sync Collections to the Lr Web and Mobile system then all that gets uploaded to the cloud system from LrC are Smart Previews of your images. Not the actual image file itself.

So please state what EXACTLY you are doing.

Is there a way to store all your photos on the external drive? Sure, YES.

I have all my images on a drive directly connected to my computer. That is what Lightroom Classic does, uses photo files that are stored on a local drive. It does not work weel if at all with image files stored only in the clouds.