Sounds like an exciting hunting ground
I hope you are going to keep your aunt in the loop and discuss what your doing and where. It's gonna take some time so keeping her and any others happy is kinda essential for such a large area with so much potential.
Make a plan and talk with her about it... also hammer out any sticking points like don't dig up the rose garden and who gets to keep what if there are items of potential value recovered.

Might sound cheesy but a written permission would be helpful especially if the relatives get gold fever and think they have a say in your arrangements with the property owner.
Hunting:
My suggestion is just to start with a general wander of the area. Take notes of where you find stuff and general depths. A moderate coil, say 8 to 12 inches, initially and pick up any junk as you go. The notes will help to isolate hot spots for later gridding with larger coils. Oh yeah... go slow.
A couple of general hunts around the main structures and a couple down the fields or what common pathways you can decipher, remember humans are basically lazy and choose areas of easy travel, should set you up with a good idea of where to get serious. Then its time for Hero Mode.
Once you've done the general hunts start gridding. Use smaller coils and get the modern stuff off the top then concentrate with larger coils for deeper finds.... dig everything. I hope your aunt will be ok with deeper holes so be neat about it. If your picking up deeper stuff in maintained areas of the property, ie the front and back yard lawns, you might just want to gps the spots and leave a token on the spot *pennies work good* then discuss it with your aunt about possible recovery.
Keeping the property owner happy is kinda paramount to having success.
Think about a partner. Preferably someone you have hunted a few times with... not your relatives or hangers on... and can trust to keep to the wishes of the owner. A partner can help cut down the time for finding hot spots and help with planning for areas of interest. Work smarter not harder
Other than that in the hunting do a bit more research, note your finds, and keep an open mind about where people tend to concentrate or work. More than likely one or more structures have been replaced at some point in time. Or destroyed and never rebuilt. Areas with a lot of iron can indicate these things. Being the site is over 200 years old some stuff wont be shallow so as I said... go slow.
Hope you catch a dream.