Terrarium controller - Where to start?

Hi everyone! I'm Dante, from Argentina. I've been dreaming with a one-system to control temperature and humidity for my snakes and plants for a long time. I always thought buying thermostats for each of my animals tanks was expensive and unnecessary, and when I found out Arduino was a real thing I got really excited about getting my hands on one. I started researching and I was overwhelmed by all the information and things on the web...so I let it go and kept wasting resources on thermostats. But...a couple of weeks ago my sisters got me an Arduino One, a breadboard and a YwRobot PS, so I have no excuse anymore. The thing is, I'm a Zoologist and i'm again overwhelmed by everything there's to read. I have no idea where to start beyond the "Starting guide". Heck, I don't know what a resistor is needed for in a circuit... So, where could I start or what should I read/watch to learn a bit about electronics and code programming needed to make my project a real thing?

My objective is pretty simple: TO be able to monitor the temperature and humidity inside my snakes tanks and, according to the temperature, switch on or off a undertank heater (just temperature for now. If I can achieve that, I'll start researching how to control humidity). I can only imagine I need X amount of temperature and humidity sensors, and a couple of relays. But that's it. I don't know If I need resistors, the Power Supply...

So, any advice where to start would be really appreciated. Thank you!!

since you are so new I would recommend that you buy a couple temperature sensors such as a 10K thermistor and learn how the inputs work and how you can read what the sensor says. Baby steps at first.

once you are comfortable reading the inputs I would highly recommend you create a separate cage so you can test your heater control. It would be a shame if you learn something and by mistake, put it in backwards and your animals did not survive the first test

One of the lessons you know, but have not yet experienced, is that sensors look good on paper, but sometimes are not able to give you the accuracy you want. the LM34 (°F) and LM35 (°C) is a great device for a project like this because it has high accuracy and your range (span) is not less than freezing and not over boiling.

most temperature controls are able to control within +/-2 deg C some can control within +/- 1 deg C, and some can do better than that.

There are three ranges of temperature. the one you hope and dream you can achieve the one that is possible with great care and experience and careful selection and help. and the one you will settle for

temperature MUST rise and fall. it MUST rise so we can tell the heater to stop heating and it MUST fall so we can tell the heater to turn on. this is called hysteresis and for a control, it is also referred to as deadband. the area that no action is taken.

what is your most desired temperature range ? what is acceptable ?

in the first post, I said to get a few temperature sensors. place them in and around a cage you have that you believe is under good control with what you have now. learn what the hysteresis for your existing controllers is. more study will give you a better target of what you need to achieve.

I would start with some basic electronics tutorials (there are many decent ones on line - find one that makes sense to you). I would also suggest a book such as "Practical Electronics for Inventors" - lots of good info on everything you are curious about in electronics, well written and very reasonably priced from Amazon. You need a basic understanding of what resistors, capacitors etc. You don't need all the fancy formulas but you do need a basic concept of what those components do (resistor typically is used to limit the current flow, a capacitor is basically a charge storage - or "flow leveler" if you will and a transistor is typically used as some sort of switch to control power etc.) Also search the forum here - there have been a number of projects for aquariums, vivariums, greenhouses etc. that all have good ideas you may want to consider.

Thank you all for your answers! I'll start with your recommendations.

I have one quick question:

If I use a temp sensor like lm 35, does the length of the cable affect the reading?

Just for experiment, I'd obtain a DHT11 or DHT 22. The interface is just power, ground, and one communication pin. And all the communication details are taken care of by the library functions for it. (Library must be downloaded and placed in "Arduino/libraries/".

I've used it plenty of times, and it seems to be very accurate.

Noted!

Do I need a wifi module or ethernet module? or that's just in case I want to save data?

Oh, also, very important.
In this kind of project, do I need resistors?