There's no import file number limitation and there should be no issues when working with 720, 1080 or 1440 HD.
2160 files can perform as well. But if a 1440 or UHD project is lengthy, or has multiple tracks and effects, you would be well advised to break it into segments...
Edit a segment, export it, view it to confirm accuracy, then edit another. When all are completed, import the segments into VP, merge them and export the final output.
At each step and routinely for any session, save Project Files AS, giving it a unique # or name, so as to avoid overwriting earlier saves. Then a project can be restored to the time it was saved by opening a VPJ file. If you use Save Project Files (no AS), the earlier file will be overwritten. VPJ files are not playable.