I was truly enjoying this game all the weekend and wondering how it hadn't more relevancy on game media... until now that I see an important flaw...
4 hours or so into the game and I'm stuck in a point where the game enemies went from easy preys in Debir to almost impossible to defeat in Scarlet Wind. The worse side of all is the game doesn't give you any mechanism to level up once all the enemies in Debir are defeated and the units at the shops are ridiculously low leveled for the enemies in Scarlet Wind.
I'm managing to win fights using and abusing of magic and the dragon but all my attack scrolls are already wasted (also, are not sold anywhere in Debir) and the dragon level isn't enough to kill a simple unit in 4 or 5 blows. My money at this point is also low because I had to replenish my units many times and, thinking the equipment was the cause of the problem, I have bought some pitiful items.
So, any advice?
Or can I assume that the point of this game is playing until you cannot go on and then start a new adventure?

There can definitely be spikes in difficulty when moving on to a new island, and going from Debit to Scarlet Wind is usually a medium difficulty spike. First off, what difficulty are you playing and what class are you playing? If you're new to these types of games then you should probably be playing on normal difficulty, and out of the classes the warrior is probably the easiest to play (due to higher base leadership, and because mage and paladin require more specialized tactics). Level of units available shouldn't make all that much of a difference- level 1 units can still be quite useful through the entire game, and can perform just as well as level 4 and 5 units if used correctly. You may need to re-evaluate some of your build choices and tactics, and I say this because you mention using up your attack scrolls. If you're playing a mage then you should have enough runes to have gotten distortion magic and possibly chaos magic by the time you leave Debir, so you shouldn't be needing to cast offensive spells from scrolls. If you're playing a warrior or paladin then you shouldn't be using much in the way of offensive magic to start with, but instead using magic to control the battlefield and buff your troops.

The only thing that can effectively put an end to the game is taking so many losses that you run out of money to hire new troops, and if this is happening then you typically either need to re-think your tactics or choose a lower difficulty.

Another thing from Scarlet Wind onward is that you need to scout the location as much as possible before engaging anything, both so that you can snap up unguarded loot (which may mean timing a dash in and out to avoid patrols), and so that you can find enemy groups that are manageable. The difficulty of those groups will vary considerably (far more than on Debir), and on arriving in an area you'll likely find some that are manageable, some that will be very hard to beat, and many that will be flat-out impossible to beat.

Deal with the manageable ones and then look at the previously too-hard ones to see if any of them are now viable targets. You may also obtain charts leading to other islands; while these may have creatures far too strong to cope with upon first arriving, you can still perform a snatch and run operation on them and thus be better prepared to deal with the difficult encounters in earlier locations.

If you're running out of money and get allready problems hiring enough troops you should start a new game.

Both games share the interesting strategic feature that winning combats isn't enough to win the "war".
You can afford some phyrus-victorys but not many or you allready lost the war without even noticing it.

Take a close look at the hiringcosts of your Units and make sure that every victory is a financial victory too
at easy and even fights.

Thanks for the advices. I'm playing on normal and as a Paladin. I'm used (or I thought I was) to this kind of games after playing FF Tactics, Disgaea, Front Mission series, etc. Beat them all even at higher difficulties when I was given the choice.
If I have to restart the game, I think I'm going to pass and try another one. I'm not very fond of games that punish you for playing one way after giving you a few choices at the beginning. It was simplier if they tell you directly to play as a warrior and force you to upgrade some abilities and don't give you the freedom sensation that this game presume at first.
I'm sorry (if a dev is reading) but I'm going to give a bad rating at this game for this.

...thats just not true, the game doesn't punish you if you play as a Pala or Mage...to be honest..i found Mage the easiest way to play the game, you just need a different tatctic/strategy to be successfull.

It's just as i startet to play Eador...i thought i am used to that kind of game but as i tried Expert-difficulty first it gaves me a big slap into my face...but after i got used to the game and knew some tactics i could use...