Sounds pretty good, you will want wider rims for those tires, you
might want to keep the stock fan tho, unless you get a real good
quality electric one.

Get a Lock-rite type of locker for the rear, as a reliability issue and
and ARB in the front, that way if the air fails you still have really good
off road performance.

As far as seats, I have an 89' Sidekick JLX, cloth seats are some of
the best I have sat in, not sure about the other trim levels and their
seats but I still like my seats after almost 300,000 miles

Please send pic of your build and of the trip, I think that would be
an awesome trip to take in a Suzuki, a trip of a lifetime

Good Luck
Wild

Sounds like your planning one heck of a trip.  Not sure if Swampers will be the best choice for crossing the desert though, they are a bit aggressive and may just dig in with the softer sand.  Then again, you might just be light enough to be able to stay on top. 

Instead of a body lift what about picking up some 2" OME springs?  Most people who run them say they are softer then stock.

Good point Drone, that many miles is going to beat on you with stock springs

Thank you so far for all the answers - regarding tires, I am open to any ideas - one of my problems is that in the past I had a lot of problems in some parts with mud ! Seems sand was never to big a issue but a lot of bad roads and mud in the rain season. It also seems the  offroad tire selection is not that good in 235/75/15 or I might just not know where to look.....
I want to leave most of the suspension origional as I fear that a lift will put more stress on the car, was considering to replace the sandart springs , shocks, bushing for new standart size ones.... I felt that a body lift would give me a bit more clearance but I am not against a spring over shackle or any other lift - I just need some help understanding it better - I feel that a 235//75 tire is all I need and as said before don't want to much stress on my components but every help is very wellcome! Please don't forget  I am new to building a off road truck myself ....

I think your choice in tires is a good one, even a M/T tire like the
BF Goodrich will pack with mud before the Swampers will, and if
mud is the problem so with a proven mud tire.

A spring lift will give you more ground clearance for off road that
a body lift, body lift is mostly to clear bigger tires, not ground clearance,
and the stresses will be more from oversize tires than a spring lift.

This tire is a good size and value, and will fit on your stock wheels

http://www.4wheelparts.com/productlist.aspx?plid=3875&catid=13&subcat=158&ptid=100816&Rim+Size_PQ=15.0&Height_PQ=215.0

Also check out the rest of the tires on their site, personally I would go with a spring lift and some 31" 
tires, and some of the most aggressive tires you can get for mud is the Interco Super Swamper line of tires

Wild

I am running Corbeau seats in mine... It's a harness ready recliner and comfortable on the long haul. I have put many miles in them (the longest was a 3000 mile road trip) and am very happy with my purchase....

As for tires.. I'm not sure on the sizes available, but I have been very satisfied with my Mickey Thompson MTZ's on my kick. They have had good grip in everything but slick clay mud (that most tires will have the same result) and they are also decent on the street. But like Wild stated... Interco makes about the best when it comes to handling the nasty mud....

If you are going to lock up the sami, I would suggest upgrading the birfield's if not the complete axle shafts.

Zig

I didn't even think about upgrading the axles, but Zukipilot has a point.  Especially if you are building it stateside and don't have to pay shipping overseas.  Trail Tough has new axles for the front and rear, add some bracing on the axle tubes from Shockworks and you should be good to go in the axle department.

If your looking at running 235/75 R15 I would probably avoid lifting it at all unless you think you will need the clearance.  Some small airbags in the back might not be a bad idea if your going to be loading it up with a bunch of weight but it does add a bit of complexity.