It is possable to get all achievements in one play through with the exception of 'Defender'(odviously), 'Battle Scarred'(just start a new playthrough with NG+), 'Gunsmith' (just continue NG+ until you can get to the cargo hold and upgrade gun), 'Veteran' (5000, really) and...... 'Master and Commander'.
I have searched all over to see if this could be possable on my first playthrough and can quite confidently say that it is a no. Two reasons.
1. I have seen the save file transfer list and with all calculations you can only ammass 7600 and change in war assets.
2. Bioware have stated on one of there forums (buried under and behind red, green and blue tape) that it cannot be done.
I have found plenty more on the subject, but them two points about sum's it up.
Now to be ready to do it all in one playthrough you must be prepared to make a full insanity run doing everything and I mean everything.
A. Import a Femshep and change the class to sentinal (also change one thing on her for 'inlisted'). This is because you will need Warp for 'Pyromaniac', throw for 'Sky high' and overload for 'Overload Specialist'. Also the easiest romance option is with Traynor who's a carpet muncher.
B.Take Liara with you at all times and use and abuse her..... singularity for the combo for 'Combined Arms'. This also makes the majority of your playthrough relatively easy.
C.You can only reach level sixty in your first playthrough by doing the following.
- Make sure insanity is switched on by the time you reach the first med box on earth. The game gives you 150 xp per med gel not used, thats 300xp per box and 450xp for wall mounted.
Do not use med gel. Ever. you need every bit of xp the box/wall gives you.
There are times that you will bump into Harvesters. Make sure you kill every last one before they fly off. This gains you another 100xp each.
If you follow these rules you should hit 50 after leaving the citadel priority II and level 60 whene you hit the final missile button before the..... erm.... end.
D. For the 'Bruiser' achievement on insanity, don't go out of you're way to get it, if you see something with low health and you can old school it go for it. Mine popped at the last battle.
E.At this level the kill brute/hyjack atlas can be challenging but I did manage them both. A bit like pulling teeth really. A relief and satisfying whene you get the 'berlip' unlock. I hyjacked the atlas at the end of the 'Gill' Grissom Acadamy whene I just used the one I was in machine guns on the glass.
All other achievements will come with natural progression and you check them off as you get them or go out of your way to finish them.
It took me fifty hours and one
minute to do all this. Time enjoyably and well spent.
Hope this helps.