With $40k of investment, how long is it realistically going to take to get a ROI?
This kind of question is a little difficult to answer.
Questions about algorithm, electric costs, electric usage, cooling, GPU or ASIC, difficulty and many more.
Stupid quick calculation on BitcoinWisdom calculator at a 2% difficulty rise and it will take 12 months+ for your ROI including electric at a decent price point for the Avalon 7.
Something as big as an investment needs to be managed and looked after too. So man hours will be plenty.
2% is absolutely unrealistic for difficulty rises as we're now seeing regular 5-10% difficulty rises nowadays. While calculators are good as an estimation, keep in mind they are estimations and are most of the time not correct.
As for working hours, supposing you use good PSUs and monitor + set heat limits on miners (which don't always work) you won't need to repair or do maintenance very much. Remember dust is your worst enemy and use compressed air to remove dust every few months on miners for optimal temps.