I've got up to Rescue Ilmarin and can no longer recruit grudgebringer infantry and have only gained the amber mage as an extra unit. Does any one else have this problem of not gaining new units?

You can recruit new soldiers/units only in selected locations. It's quite the opposite to Dark Omen when recruitment relays only on gold.

Edit: Additionally - even if you ARE in location where reinforcements should be available - its number is random. That is why in SotHR it's so crucial to win battles with min loses

It also seems to be based per unit rather than an overall pool. For instance I had a point where I could restore the Grudgebringer cavalry from four men to full strength but couldn't put anyone in the Black Avengers or the second Mortar crew.

It's kind of funny; in SOTHR men join for free but there's a very limited supply. In Dark Omen Bernhardt realizes that maybe he should offer a recruitment fee and it suddenly becomes much easier to find new recruits.

I think there is overall pool for total reinforcements, but it is sequential. Thus, if according to the game at a given point there will be reinforcement of 10 people then these 10 men will be allocated sequentially to the first units that in total are 10 men below their full strength. As such, you will be always able to reinforce Grudgebringer cavalry when reinforcements are available, but not necessarily the units that you have recruited later on.

At least that's the idea I got from recently finishing the game. As far as I remember, there are few possibilities to reinforce your troops after rescuing Ceridan till you reach Zhufbar. You need to be careful with your troops, especially if you choose to do missions near Wissenheim after the rescue mission.

That would make sense, but doesn't seem to be how it works; I was able to reinforce Ragnar's Wolves, but not the Black Avengers. This was definitely one area that was better in Dark Omen or the Playstation version (which let you distribute the new troops how you wish, and I believe had a couple more reinforcement spots, like after Shattered Pass). Yeah, the Carlsson path is really dangerous--not sure how much easier going straight to Zhufgar is but I've found Shattered Pass and the Wyvern rider to be two of the most dangerous levels, and you don't seem to get any reinforcements after Vanberg until you get past Counterattack. Getting through the gates can also be annoying (I almost got everyone through but one of the carts bugged out and caused a traffic jam. In the end I sacrificed the Dwarf warriors to get everyone else in). So far the Mortars haven't been worth the trouble and Ragnar's Wolves seem a lot worse than the 75th, though the Leitdorf Crossbowmen are nice since it's a free ranged unit.

If you've chosen the mission path that has you try to rush through the gates then try to have as many troops active as you can. That way you can order them to rush the enemy and clear a path and then rush to the gate. Less problems with slow, idiotic caravan trains then. The dwarves pay very well so it is the place you'll be making up losses and building a healthy surplus to keep you going through the lean elf employment times.

I was a little low on money at the time (a bit less than 2,000), which surprised me since I usually try to minimize costs in battle--I had a good amount after Shattered Pass but the round to Zhufbar cut through my finances.
That bugged cart seriously annoys me, too. It's like the game was angry I saved everyone and had done so well that time, and found a way to force me to retry. I don't know if the Dwarf Warriors would have left me or not anyways (I think so but am not certain), but they were a good, solid infantry unit and I regret losing them. I believe I still have a save from back then so if they would have stayed for the rest of the game, maybe I'll go back and spend some money to try saving them.

I've finished the three Dwarf missions but plan to redo The Iron Fort, as I saved less then half the Dwarves--it lets me leave Zhufbar with about 5,000 crowns but I have a feeling it won't be enough.

The key to balancing the budget is to bring along only the troops you need for each map so that you have a cushion of money built up. The Dwarves always pay lots more than you need, so you should aim to make sure your troop selection for their missions are leaving you with a healthy profit. Play it right and you can have a five figure surplus built up when you leave them. They have a mission where you get paid for each man you bring along on to the battle map, so bring EVERYONE, even if they only stand in a corner and look pretty. As many as possible (so bring the big units like Black Avengers before the small on that map if you hit the unit limit). The humans tend to pay fairly, so aim for break even at worst and a profit any time you can. There are a few obvious money maker maps for the human ones and if you've played before the easier missions become good earners simply because your skill makes up for having fewer troops. The elves pay poorly, those are the lean times, you'll need a cushion of money by then or you're playing for your life. The first time I won the game I was down to pennies and was even limited on some of the elven missions because of lack of money to even pay them to fight, so it's still winnable even then.

If you're feeling ruthless then don't be afraid to fire a unit that is too bashed up to be useful or has a better replacement available, or sacrifice them to distract an enemy and leave them to die.

Axtually, 5,000 might have been just enough if you use your troops conservatively in the next missions and/or skip the missions near Nuln. In addition, do not be afraid of firing troops. For example, once you get cannons, the value of mortars for example decreases substantially.

A thousand times this. Cannon are your friend when they're pointing at other people. Always try to have at least one on your roster. The Great Cannon is obviously the one that's the best to have.

Just checking, have you still got the unit or was it wiped out in the battle before, If a regiment gets run down to the last man its gone forever (unless sometimes you had some wounded men from the battle before)

I get the feeling that the PS version and the PC have different ways to calculate reinforcements. Not that I've played the PS much, but from the comments I've read