Welcome to the forums, Mina
First things first: I am curious as to why you want a full-suspension bike when you only intend to ride on paved roads? Do you intend to start riding off-road?
L.E. 4000 will get you a very good hardtail bike. L.E. 6000 will get you an entry-level full suspension bike.
If you are only considering full-suspension bikes, then limit your search in the short-to-medium travel category (100-120 mm of travel). If you have never ridden off road and just starting out, a long travel bike does not make sense, especially if you intend to ride it more on the road than off-road.
An essential feature to have for pedaling efficiency is suspension lock-outs or some sort of suspension "platform" that you can switch on when you don't need suspension (i.e. on the road). Even on Cairo's bumpy roads, modern MTB suspension is not necessary, and if you DO need some suspension on the road, the air in your fat tires is enough
As a general rule. Good suspension is expensive. Air suspension will cost more than coil. More adjustability=more cost.
Bike recommendations in your category of interest would be Specialized FSR XC Comp, Cannondale RZ 120 4, Trek Top Fuel, Marin Quad XCR, Jamis Dakar XC, Scott Spark, etc. Some of these models are probably a bit more than your budget limit, but below this price point you will be looking at mediocre/low-quality full-suspension bikes, and you're better off with a good hardtail instead.
As for maintenance, it is just like any other bike but on top of that there will be the long-term maintenance for the suspension linkage bearings/bushings and suspension fork and shock service (seal and busing replacement, oil levels, etc..). Some of this maintenance is very easy if you have the tools and patience to look at guides available online.
As to where you can buy these: I have never seen any decent full-suspension bikes sold in Egypt, so you'll have to import one. I recommend the US where good deals can often be had on previous years' models. If you're traveling abroad, bring one along to avoid customs and shipping costs.
If you are looking at a specific bike, post it here and I'll be glad to give you additional recommendations
