I am 80-year-old man I would like to hook up the water flow sensor with LCD display to monitor the water flow from my fluvial 406 filter for my aquarium. I watched a ton on YouTube , my question is do I need to have my computer connected all of the time to this contraption in order for it to work? I would just like to open my cabinet door and see the rate of water flow without having my computer connected ?
2nd question parts. water flow sensor, Arduino UND R3? LCD display, bread board ,jumper wires, 10k resistor also do I need raspberry pi zeros? , micro controller ESP 32? what ever these are? any thing else I should purchase
Should I purchase these items separately or buy a beginner set on amazon ? & which beginner set would you recommend this will probably be my only project . thank you appreciate any help you can give me.
do I need to have my computer connected all of the time to this contraption in order for it to work?
No, but you will need a power supply to replace the power supplied by the USB port. A 5V phone charger can easily be modified to supply power to the project. Communication with the PC is essential during the development and testing phase, but once working no longer necessary.
What you describe can easily be done with an Uno. Raspberry Pi is overkill. ESP8266 or ESP32 are WiFi enabled controllers and overkill unless you want WiFi connectivity.
Should I purchase these items separately or buy a beginner set on amazon ?
If you want to learn Arduino programming and device interfacing before you build your project a beginner's kit may be appropriate. Try to find one that comes with an instruction manual with tutorials. Otherwise, buy the parts that you need and look for tutorials on the net for interfacing those parts. Also, if we know exactly what parts you have and exactly what you want to do we can help with the hookup and programming.
I would recommend a 2x16 or 4x20 character LCD with an I2C interface for the display as those are, arguably, the easiest to interface and use.
Do you know the approximate flow rate expected (litres per minute, for example)?
Blackfin:
Do you know the approximate flow rate expected (litres per minute, for example)?
. YES 25LPM
Report to MODERATOR is NOT a reply button 
Bob.
johnjohn1212:
. YES 25LPM
Just looking for clarification: 25 liters per minute?
I would probably get tired of opening the door to see the flow rate and probably add a couple of LED's (maybe Red / Green) to show status and put them out where i could easily see them - or you could use a single RGB LED and just change it's color - there are also LEDs that are dual color. A buzzer could also be added as an alarm.
Yes these things tend to have a bit of mission creep
Good luck
"REPORT TO MODERATOR" is not for answers LOL.
Bob.