You're better off doing Overload before reaper IFF because you get Legion as you're doing the Reaper IFF mission. Then you should make sure you talk to him until his pops up. But you can do Talis loyalty mission and bring him if you want. Then you should be able to do Legions

Do literally everything you’re gonna do before the IFF. You only get one mission after, and that’s best gonna be spent on legion’s loyalty mission as it’s the only time you can do it.

You can only do one. I left Overlord and Arrival until after the final mission because I wanted to use Legion in my squad for Overlord, and Arrival fits better just before starting ME3

I would do overlord in act 1 when you are getting the first set of dossiers. Here’s how I’ve always done the DLC and to me it works best.

Do overlord DLC in Act 1…….if you do this there is a special scene in ME 3.

Then in Act 2 you can do Lair Of The Shadow Broker ASAP. In fact I would it right AFTER collectors base as there is a 5 mission count down and because to my knowledge there’s no story dialogue that will change if you did this DLC before hand…..it’s all about Liara and won’t say no more in case this is your first time playing.

After you completed the main story and saved or blew up the collector base, the arrival DLC is the FINAL dlc you should do because this bridges 2 & 3 together.

As far as the reaper IFF I am in agreement with one person that said this…..only one mission to do that’s the important one and it’s legions loyalty mission. All others should be done before reaper IFF because like you said you will start loosing people on your ship so the less quest or non critical quest you can do before IFF the better. That increases your chance of everyone surviving depending on their loyalty missions. So in short summary

ACT1: Overlord DLC

ACT2: Lair of Shadow Broker DLC

Reaper IFF

Suicide Mission (final moments of Mass Effect 2)

Arrival DLC

I did Overlord DLC this time after the Derelict Reaper on purpose... to have Legion alongside. It slightly changes to conversation.

As you do not leave the planet, you can do all DLC missions after another. Back on the Normandy, EDI informed me, that the IFF is installed and ready to use. Luckily I did speak to Legion before doing Overlord to trigger his LM, which I could do before the Collector Ambush.

The timer after Horizon starts as soon as you've recruited your 10th Squadmate. Thx to Kasumi and Zaeed, that's Tali, Thane or Samara. Like Overlord, you can get Tali, followed by Samara, Thane, Miranda's LM and then the LotSB DLC, as all start on Illium.

However, the Collector Ship should be prioritized due to the Weapon Specialisation you'll get there. In that case.... safe Project Firewalker for this to speed things up.

Literally do everything before IFF. If you have a lot of missions left, if might take 4 or so before it triggers, but it won't be enough to gain all the loyalty and assignments without sacrificing all the crew. I only held off on Tali's just to get the lol rage reactions from the Fleet as I am playing Renegade.

Which is a shame that the countdown happens, cause Legion is literally my favorite character and would of loved to hear more of his interactions but I also had to go for trophies and had 99% of the game completed before I got him.

He will continue his interactions even after N7 missions and you need roughly 4 conversations to get all info before he adamantly tries to reach consensus. So 1 after his LM, 1 aftert the SM, after any N7 assignment and maybe.... after Arrival. This way you won't miss crucial gear or XP.

I mean other character's missions or those story missions without having to sacrifice the crew by avoiding them and going right for Legion and then letting the Collectors capture the crew.