I concur with avoiding the SmartThings Sensors. They all work on the Zigbee mesh network, but the Z-wave wall switches and outlets typically cost less.
I would also advise against the Zooz 4-in-1 sensors because they have terrible battery life. If I wanted always on multi sensors I would probably spring for the Aeon Labs Multisensor 6. They are pricey compared to a standard motion sensor, but power can be provided over USB instead of batteries to give continuous sampling. This is overkill to include in every room, so I would probably do a mix of Multisensors and Ecolink Z-wave Plus Motion sensors (opt for the Plus version for improved range and battery life) or Monoprice Z-wave Plus Motion and Temp sensors
For door and window sensors I would also recommend using the recessed door sensors from Aeon labs or Monoprice unless you have a metal door. Then the door sensors are out of sight and out of mind most of the time.
Ecobee also makes the Ecobee Lite which is just like the more expensive Ecobee 3, but doesn’t include the remote temperature sensors. As was already pointed out, this can be done in software.
Lighting can be a tricky area to replace. If fixtures are hardwired to a switch, then replace the switch with a Z-wave or Zigbee switch. If you have floor/table lamps then either get controlled wall outlets or controlled bulbs. With any lamps, turning off the switch on the fixture disables the ability to control the light from an app.
Create a wall pad controller using an old tablet and Action Tiles.
I don’t have any experience with exterior cameras yet, but the Skybell HD (free video recording) and Ring Pro (free streaming but subscription for recordings) are the typically recommended video doorbells. Ring has also created a floodlight camera, so no need to run new wires or replace batteries for an outdoor camera.
Last piece of advice: install a z-wave switch near your door lock. The range on all of the z-wave door locks is terrible, so put a wired device that will act as a repeater as close as you can to it.