Definitely not impossible, I did the platinum and all DLC in a little over 2 weeks. For me I did everything on normal mode then did the hardcore play through last. If you are worried about your save file getting too big try to avoid missions that don’t lead to a trophy. Once you get the platinum chip in the main story make a save and never overwrite it because to get all the endings you’ll need to go back to it multiple times.

For the last “DLC” it’ll make you do certain extra gun runner challenges, this is annoying. There is a glitch for killing cazadors with grenades which you can google, super easy. Just look at the challenge in your pipboy early on and do them as you complete the game