I don't like to say this "more risk more return" - it is quite applicable sometimes.

The nature of the business is physical supplies - can be fast-moving or slow-moving and the selling approach will be different, you need to choose one to focus on.

Normally in this case, if you don't hold inventory, you can't sell (especially for those fast-moving type) as customers cannot wait. You may choose a slow-moving type, but make sure you target the correct market.

Alternatively, you can kick-start on project-based and use the profit earned to invest in future inventory. Just need to note that project-based also need to invest some money in the inventory before getting money from the progress claim.

Another important point to note:
"after-sales support such as warranties, training, replacement, repair/ maintenance needs to budget in"

Thus ... the first step is to know select one or two most possible approaches (like the above examples) and test them with the business model to check on business validity.

Selection and testing already very tough, hope you now have the direction, you know what to do. If you face any problem do contact for quick doubts clearance.