I first want to thank you guys for the help and support you give to the community.
As a complete newby I have a project in mind. How hard would it be to make some battery powered led lights flashing, as well as to play some pre recorded music using some tiny speakers of 8 ohm, all of this activated using a specific three or four music notes. Let's say that I want to whistle 3 or 4 notes (let's say Do, Mi, La, Sol) and by doing so I can get some led lights to flash while the music sounds through the speakers. All of this using entirely arduino. Ideally, I would power the whole thing using some coin cell batteries.
I have no idea what kind of arduino board to use or how complicated could it be.
My only experience with programming was with visual basic when I was 12 and I found it to be fun, so I am hoping that this could be fun too.
It will be too complicated for you as a complete beginner. Try some simple projects and tutorials first, which are similar to parts of your idea, so that you begin to understand some of the important principles.
Flashing LEDs is the simplest part. Even that can be difficult for a beginner if the Arduino is performing other tasks at the same time.
Playing music through a speaker using only an Arduino is also difficult. If playing only simple tunes, an Arduino can do this with a piezo-electric sounder. For real music on an 8ohm speaker I would suggest a DFplayer mini module. This will play music recorded as MP3 files on a micro SD card when instructed by the Arduino.
Recognising even simple whistled tunes would be difficult for an expert. It is not a beginner project. Can you think of some other way to interact with your project?
Coin cells are only useful for very low power circuits designed by experts. Your circuit, with sounds and flashing LEDs, will not be low power. I would suggest 3xAA NiMH batteries for your project.
This would be a hard project but a serious learning experience. ML (machine learning) would be the way to go.
I'd use the Arduino ESP32 Tensor flow library to train the program to distinguish the 3 notes. Once the tensor has been created the rest of the program should be smooth sailing. The issue is getting up to speed on Tensor Flow.
There are a small number of professionals on this forum, for example Crossroads or MsDrew. There is also a forum section called "Gigs and Colaberations" where you can offer money for help, but beware, there may be those who will take your money but have only limited experience and may not do a great job.
But if you are willing to try hard and learn, you will get unlimited free expert advice on this topic/thread.
Most starter kits include an Uno and a breadboard, which is a stupid combination, and lots of other junk that will be no use after you have done the tutorials. I have never seen a starter kit that I would recommend!
I would suggest, to begin:
At least one larger size breadboard, maybe two
A few 5mm LEDs
Some 330R resistors for the LEDs
A piezo-electric sounder
A few pushbuttons (with longer legs for reliable breadboard use)
A 3xAA or 3xAAA battery holder with flying leads or studs and a connector with leads for the studs
Hopefully you already have NiMH batteries and a charger
Some solid-core connecting wire, in a few different colours including red & black
Small wire cutters & strippers for the wire
Small pointed-nose pliers
An inexpensive multimeter
A low power soldering iron with a small bit and some solder with a flux core, 1mm or 0.5mm
A solder sucker (for correcting soldering mistakes)
All these things can be found easily & cheaply on eBay etc. Maybe post links here to what you intend to buy and we can warn you if any are unsuitable.