Although Chinese posters tend to show off and talk tough, but Chinese military is designed for defense, not offensive, yet. Just look at their H-6 series, their J-20, their ships, etc. They focus more on defense than to power projection. So I doubt that China has any plan to attack Japan.
Even if they're developing power projection weapons, it is far from ready for a big military campaign right now.
Well, depends on how you see "what's offensive capability" is
Every weapon, can be use as defensive weapon, but sometime it's no point at all to use a weapon system for defence, such as aircraft carrier, you would be better off using land air base for defence rather than an aircraft carrier, but still, you can use an aircraft carrier as defensive role.
Chinese ambition is on the rise, and that's no denying that, and as the expansion goes, there's always going to be in conflict with someone else, while as I said, I don't see that point in time happening anytime soon, but that is going to be an eventuality.
Well, they can. Japan is rich. But the question is, without raising their military spending budget, can they expand their military capability with those expensive toys?
We need to see how the situation turn out. Japan currently capped their military spending on 1% GDP, which is actually 0.98% for the last 5 years, and that number in absolute is not at all small, that's because Japan have a large GDP, and also, don't forget, that is inflated. Which mean within that 1% limit, we can see there are a lot of leeway for Japan to wiggle alone, then you put exporting weapon and future threat, Military budget will increase, and even at 2%, it is an acceptable standard for the Japanese. And even if they don't, budgeting would mean they can still get some bang for their buck with things unchanged.