Building my own estimating system out of Bluebeam + Excel — Where does Claude actually fit?

I am a plumbing contractor in Australia, setting up my own estimating business. Rather than paying for estimating software (CavSoft, CostX, GroundPlan), I want to build my own system using the two tools I already know inside out: Bluebeam for take-offs, Excel for rates and pricing.

The pricing side has to stand on its own without AI holding it together. Codes, quantities and rates do the work, and they land on the same number every time.

Custom columns on my Bluebeam measurement tools carry an item code, size and material. Every markup I place picks that up. The Markups List exports to CSV, Excel pulls it in through Power Query, groups by item code, and looks each line up against a rate database I control. Hit refresh and the priced BOQ updates. No guesswork anywhere in that chain.

The item code is the joint that holds it together — HW-CU-20 in the Bluebeam tool set has to match HW-CU-20 in the rate table, or nothing works.

It's not a flat price list either. The database is layered — each item code sits on a rate build-up (materials, labour, fittings), and taking off a fixture triggers the drainage and water assemblies underneath it, which in turn pull the penetration rates: cast-in collars, sleeves, core holes, retrofit collars, against the right service and floor. So one markup on a plan cascades down several levels before it lands as a dollar figure.

AI sits on top of that, not inside it.

That's where I want Claude doing the work I currently do badly at 9pm:

• Reading incoming emails and pulling out job details, deadlines and revisions
• Sorting drawings, addendums and RFIs into the right project folders
• Reviewing plans and flagging what changed between Rev C and Rev D
• Sanity-checking take-offs — markup counts, lengths, quantities against what's actually on the drawing
• Reviewing the cost sheet — missing items, rates that look wrong, quantities that don't stack up

If Claude got switched off tomorrow the estimate still comes out. It'd just take me longer to catch my own mistakes. That's the line I don't want to cross.

Where I'd like some pointers:

1. My take-off cascades several levels deep (fixture → assembly → penetration). Anyone using Claude to validate that kind of chain — catching where a link fires the wrong rate, or where the data needed to make the call (slab type, fire rating per floor) isn't in the drawing at all?
2. How do you keep the source of truth in the files and spreadsheets rather than in a chat log, so nothing depends on the model remembering?
3. Should I be using Claude Code or Cowork for this? I'm not a developer. Cowork looks closer to how I actually work — files, folders, emails, spreadsheets — but I don't want to hit a ceiling in six months and have to rebuild. Happy to learn Code if the control is worth it.
4. Any skills or MCPs worth setting up early so I'm not re-explaining my rates, templates and folder structure every session?

This is going to be the backbone of my business, so I'd rather get the foundations right than bolt things on later. Any advice appreciated.