1. Laravel
2. An Ubuntu VPS in either Digital Ocean or Linode
3. A managed database in one of those services, likely Postgres
That would get me to market the quickest. I have no issues with the application being in Laravel/PHP and after getting to market, I'd work on making the infrastructure scalable. I wouldn't expect overnight success, so a single VPS and managed database would let me keep costs low while I pick up a few customers and then work to handle the scalability in the background (likely AWS with a combination of EC2/ECS/Fargate, RDS, SQS, SES, CodeDeploy, ElastiCache, etc.)