As i'm working towards the last 3 achievements so my strategy is to keep 2 checklist, one to log all events at event list (link prepared by some gamers and posted at TA
https://docs.google.com/...Vi7YKUDCZzMtMVdmbEJxRUE/ (note the total no of races exclude Porsche DLC and also the last group World Championship should have 2 heats for each race such that it should be 240 race instead of 120 and in total 1299). Another list i'm reference is based on the walkthrough at TA (http://www.trueachievements.com/Forza-Motorsport-4/walkthrough.htm?page=3) for race each track (i've created at separate check list for this one).
My strategy as below:
1. Use Ferrari as the major manufacturer (i'm now level 28 for the car manufacturer still some times to reach 50 for the achievement)
2. Choose the events at event list (mark restriction off and select event valid for Ferrari in green color) and mark the event done for race each tracks.
3. Setup custom race (at online race vs AI) and race those track which don't exist at event list
4. For the remaining events which not belong to the selected car manufacturer (Ferrari in this case), i'll select another car or hire driver to complete it
Using this method, i'm working towards all last 3 achievements however it will be a bit slow as racing event at event list is much longer depends on number of lap. To organize better and keep track of the progress (you'll be mad if you keep playing this game only), I play around 1-1.5 hr each day (working towards Forza Reward as well) and hopefully i can finish the game within 2016 before they shutdown server which make race each tracks unobtainable (as the description you need to have log the time at leaderboard which mean any server down may make it unobtainable)
You'll never play alone!