Would love to hear your investment thesis on adding positions when you have a winner on your hands. Yay or nay?

I personally do not really care about diversification so having high weightage on a good stock ( adding positions) is common for me. Reason being for me a good stock should have:
1. Good resilience in good and bad parts of the cycle
2. At least 3% dividend to cope with inflation in the event I need to hold long term and <100% payout ratio for sustainability
3. Reasonable current ratio >1.25
4. Reasonable debt <50%
5. Strong operating cash flow
6. Good management

My selection is based on reasonable 8-10% return with low risk. Since it is considered low risk while selecting I think there is no issue with having higher weightage of the stock

Long-term fundamentals no change, then buy on the dip

One of the most important rule when I was starting out was to invest with no emotions. So regardless of whether it's up or down, I will just dca a fixed amount every month!

Depends on what type of investment that was and reasons you went in. Generally, Yes definitely, you want to water your flowers and cut the weeds.

Some instances where the company isn't one with high growth/potential in future, I may sell it off if there is a more compelling opportunity cost. Or if I no longer have faith/like the fundamentals of the company.

Fundamentally strong companies with wide moat can compound for many years to come. Same thing as index/ETF investing, you invest in something and ideally hold it forever. Be it pricing the market or DCA, either way you invest in it because you feel it will continue to be successful 10, 20, 30 years to come.

"Time is the friend of a great business." - Warren Buffett

Above is GOOGL's financials taken from guruFocus.com