aclr and sclr - difference

Yes you should be able to - but remember that because aclr is immediate, the blocks with sclr will come out of reset 1 clock cycle later than the ones with aclr.

Aclr should follow the same rules. Internal logic is usually best kept as active high for ease of reading. Active high or low uses the same amount of current, unlike on inter-device connections on a PCB, that are usually active low, to reduce current draw.