Modern China exhibits genuine imperialism. They've even developed and published plans for dominating world standards bodies by 2035[1]. They're crafting a gigantic blue water navy[2]. They maintain a standing army with larger numbers of soldiers than the US, to put on those ships[3]. And they have no qualms about exerting their power globally, challenging freedom of navigation at sea[4] and territorial integrity on land[5]. In their meticulous and naive way, they are most certainly pursuing a world domination strategy.
[1] - https://www.cnbc.com/2020/04/27/china-standards-2035-explain...
[2] - https://www.businessinsider.com/how-china-has-modernized-the...
[3] - https://www.aljazeera.com/news/2021/10/29/just-how-strong-is...
[4] - https://www.cnn.com/2022/07/16/asia/us-navy-freedom-of-navig...
[5] - https://news.yahoo.com/china-threatens-forceful-measures-pel...
As for the fleet and the disputes, we are literally talking about disputes between China and the US in the South China sea. All these disputes are quite clearly about China being pissed off that the US is projecting power right on their doorstep. It's similar to Russia parking its missiles in Cuba - completely unacceptable to the US. I don't think it's unreasonable for China to be looking at finding ways to challenge that hegemony.
I'm not going to try and make the claim that US and China are similar regimes- they're not, not at all. I don't beleive for a second that a hegemonic China with power similar to what the US has had would be anywhere near as good as the US has (and I'm not saying the US is perfect). But I do think there's a certain level of asymmetrical judgement here. Why is the US running warships through disputed waters off the coast of China? That seems a lot more like US Imperialism than Chinese Imperialism.
The South China Seas dispute is, in fact, primarily between China and a series of smaller nations like the Philippines and Japan. International governing bodies including an UNCLOS tribunal have consistently ruled against China's claims of sovereignty to open sea, but China keeps on doing it anyway.
That's not imperial behavior?
But you're shifting around from principles to consequentialism. Suddenly, whatever rules China breaks, even if they are extremely serious ones to do with territorial control that underlie the peaceful international order we've enjoyed since WW2 ended, it's fine with you as long as it's in pursuit of an aim that you consider reasonable?
That's a fairly blank check, innit?
this part I'm not too sure about. Historically speaking, China has been rather "introverted" as a country. They care about making sure their people are well fed and all, but seem to show a distinct lack of imperialism compared to say, the Romans, or Arabs under early Islam, Napoleonic France or Nazi Germany.