There are VAT schedules seprately for each state.. In your case, taxes are applicble in all the 4 illustrations which you mentioned in above query...
Now,
1. VAT will be applicable in case of sale in same state i.e; Maharashtra.. Here Input of VAT is also available.. Eg., You purchased a product for rs.100 on which VAT @ 4% is applicable.. Also you sold the same product for Rs. 120 @ 4% VAT... Amount payable by you is Rs.5 but you have input of Rs. 4/-... So net payable is Rs.1.
2. Here, you ill be facing both VAT and CST...On purchase VAT will be applicable and on sale CST... Sooo Input VAT on purchase can be used to set off against option 1.
3. Again both CST and VAT... CST on purchase is not available as Input.Thus, it will form a part of your purchase cost... Here you being purchaser of Goods, need to issue C form to your supplier so that he will deduct tax @ 2%. If C form is not issued then CST will be charged at higher rate i.e.; 6% (i guess... I am not quite sure of the higher %) . VAT liability will be raised which you need to setoff against Inputs if any or else pay it from Cash.
4. Here just CST comes to play.. You need to issue C form and also collect C form from your customers on sale.
Moreover, CST liability can be setoff against Input VAT if any in each month/quarter as per your periodicity of VAT filing. i.e;
Eg: VAT payable 50,000/-, VAT input 80,000/- CST payable 25,000/-
then VAT Input 80,000 (-) CST payable = 55,000/- ----- this is availabe input for VAT payable..
Inputs 55,000 (-) VAT payable 50,000 = 5,000/- ---- excess input to be carried forward for next month/quarter
Hope your query is cleared. Also refer FAQ's on mahavat site for more details/information on VAT