Hello npappagiorgio,
Thanks for using our plugins and welcome to the forums!
Do I need all three plugins on and working?
It totally depends on what you would like to achieve.
In terms of dependability: you don’t need The Events Calendar to run Event Tickets, and you need Event Tickets to be able to run Event Tickets Plus.
If you run Event Tickets (and maybe ET+), then you can add tickets to posts and pages. You can set that up under Events > Settings > Tickets.
Event Tickets Plus is an extension of or an add-on to Event Tickets.
With Event tickets you can add registration functionality to events, pages, posts so you can collect RSPVs, but you cannot sell tickets.
If you want to sell tickets, you will need the Event Tickets Plus plugin. Also note, that for selling tickets you will also need an eCommerce plugin like WooCommerce or Easy Digital Downloads.
I hope this clarifies. Please do let me know if you have any more questions, I’d be happy to answer them for you.
On your concern about large / high run time, could you please explain in a bit more detail what exactly you mean?
Thanks and cheers,
Andras