1. depends on the system you fly in. FAA, no, JAA yes.
2. isn't this the same question? FAA no, JAA yes
3. no, need to take a Multi-engine-IR
4. you can get away with one checkride in FAA, you will need to take 2 in JAA.
Usually, single engine is done first, then multi (due to costs) or even training on single engine, and a few hours on multi before checkride is possible.
-IBLB-