If you do decide to steer away from the SSD for now for budget concerns, you could decrease the performance compromise by going with an SSHD like
FireCuda instead of the suggested BarraCuda. SSHDs are Solid-State Hybrid Drives which have a small SSD cache on which the drive intuitively places your most frequently accessed files, and then also has a larger spinning storage capacity so you still get solid storage bang for your buck. Also, then if you did decide to add an SSD somewhere down the line, your performance would still be higher than you'd see with an SSD+HDD combo.
If you'd like to see how these drives stack up competitively, here are a couple of charts you can check out:
The first one compares startup times across several popular games across a traditional spinning 7200 RPM HDD, FireCuda, and an M.2 SSD (128GB). The white is for SSD, the orange is for FireCuda, and the gray is for the 7200 spinning HDD.
Startup Times
The next one compares the first 3 days of gaming storage utilization across several popular titles, and SYSmark ratings from various drive types and combinations. First of the grays is a 7200 RPM 1TB spinning HDD, second (lightest gray) is the FireCuda, third (darkest gray) is an SSD + 7200 RPM HDD combo, purple is SSD + FireCuda combo, and lastly blue is SSD.
First 3 Days Gaming Storage Utilization
Thank you for considering Seagate, regardless of which drive(s) you decide is right for your needs in the end!