Most of the "global south" will never matter. They have high population but poor prospects (e.g. Nigeria, Pakistan, Egypt etc). Why is Taiwan so important for our global economy despite having only 24 million people? Because they specialise in high-tech exports, which relatively few countries can. It's quality, not quantity, that ultimately counts.
The only country that can seriously challenge the Western system is China. India in theory wants a multipolar world but is too weak to create it without help from China. Since India view China with suspicion, that's a non-starter.
ASEAN are atypical from the so-called "global south". Their economies are actually doing well but some of them are already quite old (e.g. Thailand) and others are being undermined by Washington (e.g. Myanmar). Vietnam and Indonesia are the two stand-outs but I'm only really hopeful about Vietnam of the two.
Yes, this is the right way to think about it. Folks who don't have an economic background should read some books like How Asia Works (Studwell) / Collapse (Zubok) to get a sense of how institutions actually work/fail.
Indonesia's logistics industry is never going to be as competitive as countries like China given how many islands it has - nobody wants to build factories whose supply chains can be interrupted by a typhoon. And even if they do, its not nearly as efficient as what you have in China. Vietnam has very good prospects, but like I said, it's the population of Henan and GDP of Heilongjiang *yawn*. It's quite irrelevant in the grand scheme of things.