That level of efficiency and volume is going to be harder to manage and maintain with manual CPC if you want to scale. Not only might you need to make adjustments more frequently, but you are missing out on hundreds if not thousands of signals that smart bidding utilizes to it’s advantage. I would recommend switching to maximize conversion value and increase spend slowly per month. Start with a 10-15% increase for the next month and keep the increase steady from there month per month if you continue to see the ROAS/Revenue you are happy with.
I say maximize conversion value because as you increase budget, you may find ROAS fluctuate slightly and you wouldn’t want to limit yourself in terms of spend or throwing off campaign performance by setting the tROAS to what it is now with a larger budget. With this said, if you find you are hitting a ROAS you’re happy with consistently then you should set a tROAS consistent with what you are hitting to start and begin to scale that as time goes on as well. If you have certain products that are more successful in terms of ROAS, it would make sense to focus more on those as you increase budget. It will be harder to maintain ROAS when you increase budget by a lot (months down the road if you increase steadily) and you will want to optimize your feed accordingly.
Also something to think about (not now) further down the road is the law of diminishing marginal returns. Just something to research and bring yourself up to speed on as you continue to scale.
Otherwise, good luck! Sounds like you are off to a great start.