it has the original HVAC system (electric furnace, a/c, thermostat system etc)
$2000-$2500
I recently did this myself. Had a reputable HVAC contractor give me a estimate and it was over $7k.
Tear out the old system and put it on the curb and place a craigslist ad with a picture saying free but must take everything, with in 2 hours it will be gone($500 saved from a disposal fee, time to safely dismantle system 3-4 hours). Take pictures before demolition so you have something to reference if you forget how it went together.
Next go on ebay and match the system size you just took out(tons is how they rate systems) I recommend brand buying Goodman. You can find a ebay HVAC dealer who will deliver to your front door with a lift gate system for under $1500(local dealers will not sell to homeowners). The system will come pre filled with refrigerant, you will also need to purchase separately the copper lines (line set), thermostat wire, mastic,duct insulation and flexible duct.
Tear out all the old flexible duct and insulation on the sheet metal supply duct. Use the mastic to seal any gaps on the duct and where the new sytem connects to the old duct work. You will need to run the line set from the indoor unit to the outdoor unit but hire a pro to braze the copper and release the refrigerant. The electrical is easy enough if you do your research.
There are plenty of videos on youtube with people doing this, watch as many as you can. Don't be afraid to call a hvac company and ask questions. Even if you can't finish the install , if you get everything demo'd, new system in place and ready to be hooked up its going to half the cost of what they would quote you for the doing the whole thing. Brazing and releasing the refrigerant cost me $250 to have a pro do it.
needs 13 new windows
What is wrong with the windows? Old wooden single pane windows? Chances are what you have is better than the vinyl windows you can buy now. Do some reading on this forum about new vinyl windows. Weather strip them and caulk. Do your best to eliminate air gaps and they can out perform cheap vinyl windows.
blower motor on fireplace needs to be replaced
You just installed a brand new electrical HVAC unit why do you need a fireplace? Does the home come with a forest in your backyard? Buying firewood is not cheap. If you need some extra heat in that room to improve comfort buy a space heater ($20) and only use it when you're in the room,40 hours a month running a 1500 watt space heater is 60kwh x $0.12 = $7.20
I am sure there are some electrical updates since the house may not even meet current codes
The wiring from the 70's home probably would not meet today's codes. However unless there are some red flags this is something that should meet your needs without needing to be replaced. If there were known issues the seller would have to disclose this information. If there has not been any issues in the last 40 years there is no reason there would be new issues now.
the current owners 'updated' the a bathroom and the kitchen (although it was 20 years ago) and they put in the seller's disclosure that they 'don't know' if they got permits or not for the work. Which tells me they probably didn't and there may be things that don't meet code or need to be fixed that we don't even know about yet.
So the only clause for the kitchen and bathroom is that the work was not inspected by a building inspector? Again if there were other issues the seller would have to disclose them. For the last 20 years there have not been any issues with these home owner diy upgrades?
In addition there are cosmetic things that we want to change/update:
I think that these would be common problems with any home you look at that is 40 years old.
We would need to hire most of the work out, we are to busy.
I think long term you would be better off buying a home built after 2010. The home you described could be a great opportunity to learn some new skills for the right person. However with your busy life and lack of resources I could see this being a major headache for you in the future.