Mararic wrote...
I'm in a new playthrough, I've just gotten into Kirkwall, and I now have 'Legacy' and 'Assasin' installed.
I've googled my question, but I get answers all over the place. I normally agree with and respect the comments of the people here in this Forum. 
Sooo....when do I incorporate each DLC into my gameplay that makes the most sense? Example: I've read, " early on to get weapons, and coin". I've read, "Act III, because of better weapons, and better companion patter".
I'm not real concerned about the weapons, because I have the Signature edition, meaning that once I get to Gamlens' house, I'll have good weapons.
I've seen varying opinions on this on the forums as well, so I'm not sure how it will be of much help, but I'll share what I did and why. I also was not too concerned with powering myself up through gear or experience points, but rather the plot.
Legacy: Because Legacy deals with the family, I chose to play it at the end of Act 1. You do want to have a few levels under your belt simply because of the added amount of skills you have access to. When I say at the end of Act 1, I pretty much had everything done except for setting out on the Deep Roads Expedition, so I was level 12 or so. I also wanted to take my sibling. Yes, you have the option to take your sibling at any time, but I felt this made the most sense plot-wise. Without involving Legacy, if you have your sibling as a Grey Warden, templar, or mage it really makes it seem as if you have very little contact with them over the years as you progress. Also, taking along your mage sister makes absolutely no sense at all, given how closely they are monitored in Kirkwall's circle.
That said, I've read some things about how the dialogue in MotA changes depending on the circumstances of when you play it, so I don't know how that also applies to Legacy. They might have put in some clever lines for each sibling possibility, but I haven't had the opportunity to look at that yet.
I will add also there there is ONE point, and one point only where you have the option to go back to Kirkwall temporarily. USE IT. You will want to sell all of the junk you've accrued over the first part of the DLC.
Mark of the Assassin: Since MotA deals with Qunari issues, I decided to play it during Act 3. At this point Hawke is Champion, dealt with her own Qunari issues, and is really familiar with them and will have already formed her own opinions about the Qun and it's followers. I played this near the beginning of Act 3, after I went through all of the initial "check up on companion" quests and helped out Fenris (my LI) with his issues. Having the completed romance gave some additional banter which I liked.
I do suggest that you play these DLC while in a romance, or after having completed a romance, because it will give more opportunity for fun banter, no matter who the LI is.