Hi guys.

Been looking around the internet and nothing too conclusive - so perhaps first hand knowledge is best for the direct questions. Am seriously considering selling my Trek DS and getting a first roadie - the last time I rode one was when I was much, much younger. I've been on flat bars all my life. Few questions.
1) Fitting
So far, I've read that a 51-54cm bike should be good for me - I'm 1.73m. I read about getting a fitting done, but that's additional cost, and is it really necessary?
Also been looking on Togoparts for second hand bikes to keep the cost down, and I've decided not go with carbon but alum alloy frame instead - read concerns about cracked frames in carbon bikes that are not detectable.
2) Safety of riding on pedestrian pathways
I'm still a pavement/PCN cyclist for now - so I wonder if that practise can continue until I get to East Coast Park - a 2.5km ride to/from my place. My main routes when I go is usually up and down ECP, sometimes to Gardens East. I'd done Changi Village and back before, but all via the PCN - not entirely comfortable on the roads still. Had a friend die in a biking accident, so I'm extremely mindful about riding on roads.
- I assume road tyres will get stuck in drain grilles? Any other issues to look out for, other than the rougher ups/downs?
3) Adaptability
Is it easy for someone who's used to a flat bar and the relaxed posture to adapt to a road bike? Also, is it normal for people to cycle with MTB SPD pedals on road bikes (which I am used to)? I notice most people seem to wear SPD-SL pedals/shoes, which are a little difficult to walk in, particularly since I intend use my bike for commute too.
4) Any good bikes to recommend that are lower priced? Preferably those with not too aggressive riding postures too, if such a thing is possible. Or should I stick to trawling TGP? Am looking to get 105 class components at least, something to last a decent amount of time.
/Dan