Hi Ambrish,
Do you need an ADSR? At the end that's up to you :-) That's the beauty of a modular synth, you don't have to do anything you don't want ;-) So, you could follow up on Defragmenteur's advice, that saves you for the moment an ADSR however, I do think that sooner or later you need an ADSR but then again, looking at your rack you might need other things as well like a filter, LFO, another VCO, etcetera. But that it easy on that since your limited space and follow Defragmenteur's advice. Once you have build up more experience with the A4 and your rack then it will become clearer to you what you are still missing and then go for that.
Good luck and kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads