I'm surprised you haven't found definitive answers to these questions, here on GeoExpat. As you say, the points have been discussed ad nauseum. Still, here we go again :
1. Realistically, your chances of finding a job are pretty good. There; you have a definitively good chance.
2. The truth is, more experience and better qualifications will get make a wider range of better-paying jobs open to you.
3. Yes, but see point 2, above.
4. A weekend TEFL is of limited use, but that is not to say that it is of absolutely no use at all. It may help with some tutorial centres and it might well give you some 'hands on' experience of what classroom teaching is like.
Give it all some perspective. You're probably going to hear people say that if it isn't Trinity CertTESOL or Cambridge CELTA then it isn't really worth the paper it's printed on. But is EFL teaching really your long-term goal? Are you really going to be looking for a stable, well-paid, full-time teaching post?
On the question of experience, I'd stick my neck out and say that qualifications are more important. If you have a fresh graduate who has just completed a CELTA and is looking for a first job, and you also have a candidate who has been teaching in a variety of language centres for two or three years without any qualifications whatsoever, then my initial reaction from the point of view of a prospective employer would be more favourable towards the untested yet qualified candidate. That's just me, though. And if you have two equally inexperienced candidates, then naturally you'd favour the one with qualifications (though other factors, such as ease of getting a visa, strength of regional accent, skin colour, charm and personality may all contribute to the final decision).
Be aware that there are plenty of opportunities out there for those who are willing to work for peanuts. On the bottom rung of the ladder there are tutorial centres that will dither about your visa. Feed you a load of cr*p for months on end about why your visa hasn't come yet. You end up chucking it all in when you don't get paid for several months. Then you come back to these boards and say something like "My employer hasn't paid me since November and still hasn't sorted out my work visa, despite the fact that I've been teaching in his centre for nearly a year...", and on the next thread down there'll be someone asking "Hey, can I just rock up in HK without any qualifications or experience and just walk into a job?". And we begin it all again.
Don't let this put you off, though. If you qualify for a working holiday visa, then this may help. If you have a good way with people and are resilient then you'll be ok. A sound legal basis for being here and working here is highly recommended, however if you work the tutorial centre circuit then you will probably meet a fair few people who have been teaching in Hong Kong for a while without the proper paperwork and who are quite blasé about the whole thing.
If you do start teaching in HK without one of the more widely recognised qualifications, and then later decide it's something you'd like to take further, then there are courses you could study here. But having said that, you might want to consider applying for a PCLL course and getting into law. I know a teacher on the NET scheme who is doing her PCLL part-time, right now.