One missing fact could change the whole calculation: does £3,773 assume the duplex is let under one tenancy or room by room? That affects turnover assumptions, management intensity and who is expected to cover council tax and utilities. I’d also establish the tenure and whether there are service...
At 4.7% gross, I would focus less on choosing a target net yield and more on how quickly ordinary costs consume the spread. Insurance, tenant turnover and re-letting expenses could matter as much as routine maintenance. Test the result with a meaningful vacant period plus a major repair...