Answer to your first question is: "It depends". For example, if the Madhya Pradesh High Court has issued a direction to the Madhya Pradesh Government on a particular issue, that will be binding on MP Government only and it will not be binding on other State Governments (for example, Gujarat Government) for a similar issue. On the other hand, if the MP High Court gives a direction to the Central Government, it may generally be binding on it for the whole country though sometimes (depending upon the issue involved, such as an issue of local importance only, say for a particular river in that state) it may be binding even on the Central Government also only for a limited area.
On the other hand, an order of the Supreme Court is generally binding for authorities in the whole country, unless if it is issued only in some local context in the facts and circumstances of the case.
Your question No. 2 is not clear. But, if you mean to ask as to whether the HC can be approached through PIL in respect of a violation of an article of the Constitution, then the answer is "yes".