Like the others point out, SSDs are very expensive right now. To realistically get a 1TB SSD you’ll have to wait 2 to 3 years. If you want that size of hard drive I would go for a high RPM HDD. Many people who do use a SSD will have it hold the OS but use a HDD for the main storage.
On the second question, the easiest way to transfer everything is to use a Hard Disk Cloning device like this one17–155-602-Product
I used it to upgrade my laptop (2.5”) and it worked great. If you have a 3.5” drive you’ll want a different model. Pretty much you put the new drive in the enclosure and connect via USB and run the software. Your current drive gets cloned exactly onto the new drive, and then you swap the drive out. You can then use the enclosure with your old drive as an external hard drive for backups, additional storage, etc…