1,Good, you're nearly home. It would probably be best if you would use a third-party partition management program, e.g., MiniTool Partition Wizard (or one that you may be otherwise familiar with) to merge the two resulting partitions into a single partition.
2. Two caveats...
A. Do not make any changes to either one your present two 2 TB HDDs until you're assured the merging operation was successful. You want a "fall-back" position in the event the merging operation fails.
B. Since the merge of the two partitions will result in a single partition having its own drive letter assignment, it's possible that certain programs/applications contained on the single partition will not be able to be accessed by the boot drive. Possibly a simple change in drive letter assignment may resolve this issue or you may have to even reinstall the program.