Don't know the Mac, but have you thought about using Access or something similar? Either by itself or in conjunction with Excel?

Access to do the Client and Job tracking, and Excel to do the estimating


It seems like there's a lot of un-normalized data and you have to enter a lot of information more than once


You could have a series of Userforms and store data on a worksheet: you only see the UF, not the WS

Example: UF_ClientMaint with Add, Update, Delete buttons to retrieve or store data

I see linked data tables for Clients, Jobs, Required Equipment, etc.