Real estate agency seeks construction software (calculation, quotation, billing)

We are a real estate agency and invest in new buildings (turnkey construction) and renovations of residential and commercial buildings. We act as a general contractor and work with craft businesses (all trades) as well as architecture and engineering firms. We also sell real estate. 

The software we are looking for should meet the following requirements:

• Import offers => be able to calculate a surcharge for each item
• Must cover all trades in general (electrical, plumbing, drywall, painting, etc.)
• Position-related surcharges, must be able to calculate a percentage surcharge on each item if necessary => Send quote to customer (e.g., buyer of condominium)
• Quote to customer, add quotes (e.g., from plumbing) => Quote to customer (e.g., buyer of condominium)
• Measurements and billing to the customer after order fulfillment
• Billing to customers
• Manual entry of invoice number
• Should also be operable from a tablet on site, at the construction site

One software workstation is planned. This means one license for only one employee. They would then want to use this for their PC, laptop, and iPad. The computers (PC, laptop) run in an MS Windows system environment. The mobile devices run on iOS.