Maxing out skills

If you grind... all of them.  AFAIK, there is no actual leveling cap on the first playthrough.

For comparison:  There is a Level 50 cap in ME1 for the first playthrough.  The game only lets you get to Level 60 after you've beaten it once (that is, have gotten the achievement for beating it once).  After that, the game lets you reach Level 60, but the XP available to you in a single playthrough (without using a glitch) is insufficient to get there unless you've imported your Shepard into an NG+ game.  To reach Level 60 in a second playthrough, I believe your Shepard has to be higher than Level 47 (although I've not thoroughly tested it).  You also have to kill virtually all enemies on foot (i.e. not while inside the mako) and that second playthrough has to pretty much be 100% completion.

ME2 and ME3 let you get to the highest available level in one playthrough (Level 30 for ME2 and Level 60 for ME3), but that level was insufficient to max out all the skills. 

In ME:A, the maximum level is 132 (that is, the game stops accumulating XP at Level 132), which is more than sufficient to max out all the skills.  Enemies do legitimately respawn in many locations, so there is technically no limit on how much XP is available during a single playthrough... you'd just have to grind the killing of these random enemies to acquire it.  Of course, the better choice is probably to just start a NG+ game.   I had no trouble getting to Level 132 doing two 100% completions of the game.  For people who tend to drive by the random enemies that spawn when on the way to a specific quest marker, it might take 3 playthroughs.

The choices are all yours.