Choice of microcontroller for garden monitoring project

Hi, I'm just starting to read on Arduino and glad to see the community is strong! I would like to use this technology for an indoor garden project. I have sufficient basic electronic knowledge but no significant programming experience.

First, I'd like to know if this is a realistic project for someone eager to learn Arduino and secondly, which microcontroller would work best (or microcontrollers if more than one)?

My project would consist of the following elements:

Four temperature sensors monitoring four COB LED heat sinks.
One fan per heat sink, each fan's speed controlled via PWM wire and turned on/off by transistor and powered with external 12v supply.
One temperature and humidity sensor to monitor room.
Data logged and stored on sd card.

Excluding the microcontroller, here are the major components :
1 x 12v 2A power supply
4 x Noctua SF-A8 PWM fans (12v 80mA)
4 x probes made with TMP36 sensors
1 x DHT22 humidity and temp sensor
1 x LCD 20x4 or a larger TFT lcd
1 x MicroSD breakout board
1 x Real time clock module

Future add-ons if I can get the first part working:

Water temp and level sensors (4-6 count)
Larger lcd to display all this info
Turn on/off appliances depending on environment temp/RH.
Time lapse camera.

Components:
Up to 6 water level float switch
Up to 6 waterproof temp probes
Up to 2 SSRs to control appliances
1 x TTL camera w/ infrared

So in which Arduino board should I invest?

Good day everyone!

Get an Uno to get you started - later when you got the parts working you probably want to solder it on a protoboard for more reliability, and then you'll probably want a Pro Mini or a Micro, and then you can use the Uno for the next project before adding that to your existing rig.

Oh, pro tip: get a spare (or two) right away. Good chance you will destroy a board when miswiring or so. That's just part of the game.

I'm under the impression that a Uno doesn't have nearly enough analog and digital pins for the first part of my project.

All four fans are operated individually and associated to a different temperature sensor. I don't want to assume all heat sinks will need equal amount of cooling all the time.

I would start with an Arduino Mega
use an LCD with an SPI intrface to reduce digital pin requirements
use relays to operate the fans
if you require more digital IO use an IO extender

Add up all the pins you need (sorry, can't be bothered to do your homework) and see whether it fits on an Uno or that you need a Mega.

One disadvantage of the Mega is that it doesn't have a version that you can actually conveniently solder to. Not good for (semi)permanent installations.

Mega. With this sort of project, you can run out of memory before you run out of pins anyway, and you are likely to later need more tomorrow for something you haven't thought of yesterday, so you might as well get a Mega to start with. Also, while I'm not so sure a Mega is vital for a larger LCD display these days, it probably broadens your options. You justify the 12v PSU, but you should also consider running Arduino therefrom via decent 5v regulator.

I would start with a few NANO's
I like the two NANO shields that offer different wiring. one has screw terminals. the other has lots and lots of pins.

as for the high pin counts, look at two NANO's, they can talk and control at the same time.

the Beauty of the UNO is the shield use.
Getting two UNO's offers one for your display and one for a RTC board with SD card.

As a note, for an indoor garden, your temperature control could be by DS18B20, a simple to use, 1-wire sensor. the 1-wire bus can hold more sensors than you might need. these come in 1meter, 2 meter and 3meter cable legnths if you look around for them.