Hi Arjun
1. Machine Coding for SDE1 is as simple as general Leetcode problem. You don't have to make classes or develop frontend. I will try to post the code in a day or two. You can have a better understanding from that. Only one thing is that your code should be easily modifiable to entail any further changes, and it should adhere to one function one responsibility principle.
2. I have done a few problems on Leetcode, that too which I find are intriguing. Doing insanely huge amount of problems won't help. My main focus has always been to learn something from every problem that I spend my time on.
3. I had been active on Codeforces since April 2020. Apart from that I do read about software development. I only prepared on those things which I thought I was weak at like Java OOPS, OS, DBMS.