Demand, hands down! Here is how I would do it:
1. Pick a niche service specialty. If you're just starting out, determine which service speciality can get you the most early traction through secondary research. Make sure your basic premise (macro-level thesis) is solid.
2. Create your customer persona
3. Validate that by speaking with 30 prospects (or a statistically significant sample size).
4. Pivot (if need be)
5. Build your supply and create liquidity
6. Generate transactions and ...
I can go on about this, but I'm sure it will be never ending. Happy to talk more about this, if it would help.