So I would really like to be able to use the full area of the attics when I rebuild this place.

Basically I want to use a system for the roof that will allow the attic to be finished at some point in the future if so desired, even if not and only used for storage, it will be part of the conditioned building envelope, and sealed without any more ventilation than anywhere else in the house.

To achieve this the roof needs to be designed differently, here is what I had in mind. Granted i understand there are many complications in materials such as ridge vents, these are assumed.

Top to bottom;

roof shingles
underlayment
sheathing
2x on flat edge air gap spaced 24" o.c. corresponding with rafters
rigid foam XPS (how many inches I don't know)
Purlins if needed (if thickness is greater than 1 1/2 inch)
2x rafters
Collar ties

Now what I'd like to do is add loose fill cellulose between the rafters. But I'm not sure how to install it really, which is probably easier than the design of the roof itself, all I know is that i thought you were supposed to use some mesh or whatever, but the collar ties would get in the way and it's late so it is blowing my mind and I can't figure out how in the heck to get the cellulose in there... heh (wow that turned into a run on sentence huh, lol, yeah it's def time for sleep.)

Your system seems overly complicated. Why not just use a SIPS system, or spray foam between the rafters.
Forget the XPS, purlins, loose fill cellulose, mesh, etc.

Read & understand this before proceeding:

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

You may or may not need or want ridge vents, but the double-roof deck approach is usually required when applying foam over the top of the original roof deck to allow drying & draining of any leak water. I doesn't need to be a 1.5" air gap- 3/4" (1x furring strips is enough- no need for 2x). If you used SIPs, you'd need the air gap as well. (IIRC this is advised anywhere that gets 20" + of rainfall /year, or anywhere that snow will linger on the roof deck.)

Spray foam tends to be cheaper per unit R-value installed than sheet goods, but if you're going with the roof overlay approach, both ISO & EPS are cheaper than XPS per R-value. EPS or ISO pre-laminated onto an OSB nailer deck (sort of a half-SIP) is available, usually sold into commercial space. ISO results in thinner assembly, if you're going for maximum R. A 3" layer of ISO is ~R20-21 whereas 3" of EPS is ~R12, 3" of XPS ~R15. I confess I'm partial to ISO as retrofit roof deck insulation- save the XPS for where compressive loads are higher, EPS where you have a lot of space to work with. EPS is cheapest though.

Nailer-decked high-R panels like this can make for a simpler assembly:

http://www.atlasroofing.com/tabbed.php?section_url=58

Long-screw them to the existing roof deck, apply a layer of roofing felt (liquid-applied versions, if you like), lay down your furring strips wherever you like atop that for the upper deck.

Blow-in-bag method works for cellulose between the rafters, but it's better to use wet-spray (which has a water-based adhesive) when you do rather than dry-blow or it'll shift & sag over time. If you have the budget for it, 3/8" or 7/16 OSB on the interior of the rafters will allow you to drill & dense-pack cellulose. But when it's all said & done, it might be cheaper to blow half-pound foam between rafters for a similar R-value. Whenever air & vapor-permeable insulation is used under a roof deck, be sure that the insulation OVER the roof deck is high enough that the average wintertime dew-point temp stays within the foam layers lest the roof deck become the condensing plane, with ensuing rot issues.

I see your point with the option of a sealed attic and open cell foam. This method has not been around for a very long time though I thought? I didn't know the long term durability of it, and I want everything I take the time to do on this house to last 100 years or more. Another factor is that frankly I'm a bit skeptical of the long term health effects of spray foam. Also it's price per square foot, if it came out relatively the same, even though a ton more work, i would go with the cold deck and extra work. Foam while an option for everyone, I personally would like to use as little as possible, even if I am being retarded.

SIPS are an option that I did think of, I would have to cold deck that too though, and I just assumed that SIPS were going to me more expensive anyway, although I really honestly have no idea what SIPS cost.

As far as ISO goes, i was not sure it would hold up as well if it got wet as the XPS would or if it's strength was really adquate where there would be 2x or 1x purlins pressing on them. Also considering I haven't actually build the roof yet, i thought about ripping plywood or osb and running 1" strips up the rafters for the backing to the xps to cut down on some of the cost, again wasn't sure if that would be enough to support it though.

I'm going to have to digest the rest of that info, got to leave here for now, any thoughts in the meantime are welcome

btw, thanks for the input Dana, was hoping you would drop by my thread, i've read a number of yours and a few other's posts that i wanted to share knowledge with.

The best design approach by what you've described, is to not think of it as "attic space". It's living space. That's how the designers-- and building inspectors-- will look at it. The floor needs to be designed for 40 psf living, not the typical 10-15 psf for light storage.
Once you do that, you'll see that it doesn't need to be vented. If you have HVAC, up there, or toilets vented to the attic space that needs to remain attic, do that separately.
Unvented roofs over occupied space are done in commercial work all the time. You might want to check some of those out, or go with what Dana1 or aeridyne described.
But have your SE, or at least a GOOD architect go over it.