Leaving room for expansion can be useful, especially when you are still learning which resting positions your cat prefers. Start with a complete, usable route rather than a few disconnected pieces that depend on future purchases.
Check whether additional components are genuinely compatible with the same product system and whether the wall offers suitable mounting positions. Keep the original instructions and measurements so later changes can be planned accurately. Avoid promising yourself an extension across a window or doorway before assessing the clearances and support. It may be better to add another low resting area than to increase the height. Observe which parts the cat uses over time and let that evidence guide the next purchase. Expansion should improve access or choice, not merely fill every available section of wall with furniture.
Keep an annotated sketch of the current mounting locations and the unobstructed areas beside them. When considering an extra shelf, check whether it adds a new resting choice or simply duplicates a space the cat already ignores.
For product comparisons alongside this advice, see SkyRoute wall climbing set and Feline Sovereign Spire. The details below explain their sizes and uses.
Further reading: vcahospitals.com; cats.org.uk.
SkyRoute wall climbing set
Feline Sovereign Spire