I have normally seen fruit concentrates/puree added at high krausen, maybe 3 days into fermentation. Typically, fermentation kicks back up for a day or so as the added sugar is eaten. An advantage of this is that it allows you to rack your beer twice (into secondary and bottling bucket) to eliminate any particulate transfer.
If you want to add it to secondary, I'd probably add beer first then the puree. I don't see a need for straining...any fiber/particles will settle out along with flocculating yeast, proteins, etc.
I made a citrus wheat earlier this summer and have been drinking it for a month or so. I feel that the citrus aroma/flavor has faded a bit. I'd be concerned with losing flavor and aroma from leaving it in secondary for that long.
I don't think racking to your bottling bucket will be hard. Wheats are supposed to be hazy anyway. Since your are carbing in bottle (I presume), there is the expectation that you will have some yeast/material in the bottom anyway.
I have never used that yest, but its website says it is non-flocculating. Have you had trouble in the past with the yeast not falling out/down after fermentation was over? Do you use any fining agent? I think your yeast would be fine, but I'd add a whirlfloc to the boil. If your beer is too hazy/thick/has peach pulp in the secondary, you could cold crash before bottling. If you went that route, you'd jsut have to plan for more time to bottle carb.