Maybe you can add instant charge for medics? That helps with a lot of achievements. Or is that already included? You could do it only for blu, or only in the blu spawn room if that isn't possible.

Maybe add indications on the capture points which tell you how long that one is. minor point.

Maybe change the 10 second capture point to a bit longer for complicated achievements on capture points.

There is also use for a payload car, but i guess there is a good reason for not having one in.

Maybe make a small risen platform that makes it possible to get fall damage. Handy for a small amount of achievements.

This last idea would be actually very handy, but i think a lot of work to make. I think it's best to make it now and then wait till all the classes are released, or just wait with it alltogether.

Number all the 'things' you have in the map, clearly visible and in a logical sequence. 

Then, for instance on the wall in the blu spawn room. Have a pic of each class, with next to that, all the icons of all the achievements for that class, with next to each icon, the number of the needed thing, and maybe other things you need (eg. a blu medic and a red demoman). Together with the new feature to show achievements on your HUD that would be awesome imo.