Questions related to order operation

1. When exchange rejects the order, what event we'll get?

2. How to get the latency of new order registration or cancel a placed order?

3. Is it possible to place a single order that contains multiple pairs of trade? (securities)
e.g:
- ETH/USDT, SELL 0.001 at 270$
- BTC/USDT, SELL 0.000001 at 8000$
- ...
Put them all in one order.