Thanks for sharing. That sounds like a great idea. You create a pie with fractions matching the holdings of an ETF. If one company, say AMZN, increases its proportion in that ETF because its market cap goes up more than average then one rebalances - but effectively this just means just keeping the ratios of shares bought and sold in roughly constant proportions. ETFs do not need to rebalance: they just buy and sell shares in fixed proportions, like 4 AMZN shares per 5 ADBE shares - excepting when companies go in or out of the index or change their number of issued shares.
There are two simple ways to construct a pie. (a) choose 10 companies, say, and then buy them in equal value weights, (b) buy them proportional to market-cap weights. Most people do (a), whereas index ETFs do (b). Studies have shown that (b) does better as it is somewhat benefits from a momentum investing effect. Personally, I did this recently with a small self-made ETF of ADBE, AMZN, GOOG and V. I bought shares on Trading 212 in ratios of 5:4:6:16 which meant by-value weights of 0.08, 0.42, 0.36 and 0.14 (which I sourced by looking at the contents of SPY ETF). Fractional share were great for doing this as I did not want to buy a whole AMZN share at a time. In hindsight, I have been very glad to have had 42% in AMZN, though the 8% ADBE has done well too.
A portfolio of equal weights is also good. Many portfolio managers think that way and suggest clients are well-diversified when owning 30 companies in equal weights.