multigrain bread, baker's percentage, and hydration

I love love multigrain bread as a daily use bread but I still haven't found that perfect mix. I have tried a couple different recipes from Peter Reinhardt including his multigrain extraordinaire and a couple different recipes from Crust and Crumb, and those are good but not quite .. perfect.  Recently I tried a couple of Hammelman's recipes and still, not there, so I've decided to just try and combine what seems like good elements from all and come up with my own formula.

I use a 1.5lb loaf pan and I can usually get a good size multigrain loaf from around 900-950g total dough weight, so I'm using that as a rough goal for a final dough weight ...

I like about 20-25% of the total dough weight in grains (soaker), and I think these breads really do need a higher hydration to account for the increased absorption, but I'm finding it hard to do the calculations because I don't really know how to account for the multigrain blend soaker...

so for rough numbers, I can start with 400g of flour, 300g of liquid will be 75% hydration but if I use 200g of grains, that will get me pretty close to the desired dough weight but how does that affect the overall dough hydration? Also, this dough will be enriched, not a whole lot but I will very likely use either milk, honey, buttermilk, or some combination of those with water (still working this out), does that change things too?  I might end up with a wild yeast instead of commercial, but I can figure out that part, my starters are either 100% or 50% hydration for the ease of the maths, so I'm not going to worry about that bit yet, I just want to know how to factor the grains into the overall bigger picture.

I do realize as well that grain absorption can vary wildly - so far I've had to add a little bit of water to the dough to keep the hydration up, so at least for me my grain mixes have tended to absorb a pretty high amt of water. still, I know that I'll have to do some experimenting with that in mind, I am just looking for some basic guidance, some notion about whether to start with hydration percentages in a multigrain loaf. 

oh and I won't be using 100% whole wheat, it will be a combination of bread flour, WW flour and a little bit of dark rye flour. at least 50% bread flour.

also, any thoughts on dough enhancers or vital wheat gluten as additives for this? I've never used either but it's a thought to help with spring...

thanks in advance