Hey there. Agree with Bosvaark re. taking a close look at your workflow before putting anything in hand. I'm a carpenter and use iPad for all my work-related notes, calendar, sketches, tasks, job costing, estimating and invoicing; I think you'll struggle to get everything you're looking for in one app tbh - I'm a one-mand band and I use a variety of apps to handle my needs.
FWIW, Informand HD is good for Calendar, Contacts, Tasks, and notes. I use Notes Plus for any notes that also require simple sketches or plans, and Simplenote for basic text notes. MagicPlan for room layouts, Quick Sale for job costing, estimating and invoicing.
You can use also GoodReader for annotating PDFs, though other specific form-filling apps are available.
HTH, Pete - and let us know how you get on!