Finally! Just got myself a Nex 5R with SEL1650.  Got this to complement my alpha 550 + tamron 1750 + sal50f18 + F58 as I want some mobility instead of lugging bulky camera equipment everywhere.

I still love my a550 especially together with the f58 flash.

My question is, if I want to utilize the f1.8, is it better for me to buy a EA-la1 adapter (to fit the sal50f18) or just buy a SEL50f18?

With EA-LA1, autofocus should work on my sal50f18 (but not my tamron 1750) because it has SAM right? 

Note : Anybody knows where I can get cheap cheap EA-LA1? (Preferably 2nd hand) 

You have existing A-mount lenses, therefore get the LA-EA2 adapter.  I just don't like that protruding hump . I suspect your A-mount Tamron 1750 should AF as usual on it.

SEL50f1.8 is excellent, I have it on almost 80% of the time for Cosplay shoots.  The downside is the slower AF and it's not a Macro lens.

In event halls, 50mm will force me to stand further away for a full body shot. The problem is.. many other photographers with shorter focal lengths will block me (stand in between) and I will have a hard time getting a clean pic. Oh well...  I sometimes think the 35mm is better in this respect.