I live in a 3500sf home (2 stories) and I faced a similar situation to you @M_Li. Where do I start? What areas do I cover? Bulbs vs switches?
So, I started with the areas that my wife and I use most often. I essentially created a path from the kitchen and great room to the bedroom and game room, because we are in those areas more than any others. Then I converted the outdoor security lights. Then I tackled the guest bedrooms, starting with the ones that are used most often. Then the bathrooms, mudroom and the walk-in utility closet.
I still need to work on some larger walk-through common areas (10x20 foyer, and hallways due to 4-way switches) and the study.
I basically followed what I thought was a common sense approach.
For the 2-story family room, I replaced the switches, so I wouldn’t have to deal with the 15-ft high bulb replacement. For the kitchen, with recessed lighting, I did switches as well. Essentially, any area with multiple lights on the same circuit, I replaced the switches. This also applies to the outdoor security lights.
For the bedrooms, I opted for motion sensors and RGBW bulbs in the lamps, while leaving the overheads for later upgrades when I decide to automate all of the ceiling fans. This allowed me to automate the lighting on motion, change the color temperature and dimming based on time of day, and use a color (red) for a night light when someone gets up in the middle of the night. I found that red was less likely to wake up the other occupants in the room.
The bathrooms, walk-in closets, pantry and mud rooms didn’t really merit full automation. So, I installed occupancy sensors in all of them, except the water closets in the bathrooms. I also installed occupancy sensors in the garage work area.
All of this was a combination of Z-Wave, Zigbee, WiFi, and IR (some of the unmentioned accent lighting is IR controlled by Harmony Hub in order to avoid the cost of Hues while getting the same ambiance), as well as non-connected motion sensing lights on the stairs and the above mentioned occupancy sensors.
This darned near covered my entire house. So that will give you an idea of how far you can go easily on a first pass.
I would probably advise taking some time to see how you live in the home to decide what you want automated and what can wait. Flesh out those scenarios, and then you can start filling in elsewhere. Just finding reliable devices and building your automation routines will be enough to keep you busy for awhile.
As far as range, I have a Zigbee contact sensor in my mailbox that accurately communicates with my hub approximately 40ft away. Unless it’s a 3000sf Ranch, you shouldn’t have many issues, as long as you install Zigbee repeaters (outlets, switches and some bulbs can do this).
Bulbs vs switches is probably something you will ask yourself repeatedly, and even your answer may change. The question is extremely subjective. The answer usually comes colored (pun intended) by your lighting needs in each application.