what worries you the most?
First of all, always whether the money will be enough. But even Rockefeller would consider how to proceed strategically in the best way. You should always focus on the must-haves first. Although the plan is made for the entire property, outbuildings and Pfirlefans come last.
I would only clear out the monument and secure it against any potential damage (roof, moisture). Otherwise, it stands well and can look nice until it's its turn.
I wouldn't attach the new house either but plan it as a separate freestanding object. At least depending on what the area and setback rules allow. I haven't looked that closely yet.
There are several reasons for this. First, you are on the slope. Building somewhere there always causes trouble with the heights. Second, the materials will almost certainly not match. Both visually and technically, that would be an unnecessary hassle. Third, an insulated construction would be advantageous in case you want to rent out the monument at some distant point in the future, in order to preserve the privacy of the rest of the property.
Therefore, in your place, I would certainly create an overall plan to represent the final division of the property with all paths, parking spaces, etc. But for the actual construction, I would initially focus only on the new main house and optimize it. Just the demolition/disposal and preparing the building site probably costs around 60K already. Of course, it's hard to estimate. If it gets complicated or ugly materials are found, it can be even more expensive. If you're lucky, it can also be cheaper.
Add to that the presumably 3-story construction, slope stabilization, possible development work, all contingencies regarding water from above, below, and through piping, zoning plan requirements, and property work. We don't know your needs that precisely yet either. Depending on the region, the 700K are already completely spent on the main house including garden.