New Player need advice on Campaign mode...hit a difficulty spike

You probably just need to persevere and try different gear and strategies. The team you have (dwarf warrior, human priest and wizard) can beat the entire campaign with no changes - I know because I did it. But some missions are tough and require figuring out.

 

The advantage of a 1-1-1 team is that you get to know the pros and cons of all classes. Knoweldge beats any equip you can drop, even a VP.

Also I don't think it has been told, but I could clear many stages the first time I beat the campaign with just the priest remaining alive who hit (with vamp attacks) and ran. In solo mode, with just a character, priest is the best.

 

Check Randimar's, if they have anything with firestorm on it, buy it.

 

I'd second Questor, Sir Veza and Stexe here.

On reading this I went back to retrain some new units and ran up a party of 3 Humans; 1 Warrior and 2 Priests. I had the benefit of some decent equipment, but I would certainly say that Priests have a lot of firepower early on. They do not have the multihit fighters can bring with Chop cards, but it is fairly easy to get Priest weapons with abilities like:
Violent Swing, Controlled Overswing and Punishing Strike. I haven't peeked past level 10 yet, but up to 9 these attacks are fairly mean. 10 damage one-hits or is instant red for a lot of creatures. My Priests rolled out with:

Martyr's Pick: Violent Swing for 10 damage to the face, Reaching Swing for some range and blunt-immune enemies and Bad Medicine to get a DoT on full HP enemies.
Feathergod Blade: Controlled Overswing for 10 more damage to the face, Draining Touch for self heals and Stone Feet for 3 turns of 1 additional armor.

and

Wrathful Club: Punishing Strike can hit very hard if used on an enemy that hasn't taken its turn yet, and Draining Touch
Holy Stone Maul: fairly weak, but it does have a Violent Swing and Bad Medicine

Plus, between the two Priests' other gear I had:
2x Holy Presence
1x Healing Spirit
1x Help The Weak
1x Healing Benediction
1x Healing Blessing
2x Twin Heal
3x Heal

... due to all the overlapping HoT effects, I've ended some battles with full health, especially since they both had a lot of vampiric attack/heals like Draining Touch, Sapping Touch and Invigorating Touch.

My Warrior had some decent gear, with a Thick Club and Obsidian Club, but he couldn't match the Priests' firepower and buffing. I was very surprised just how much damage the Priests were able to dish out and soak up with decent armor and healing auras.

So I would definitely say try different race and class combinations if you get stuck. If nothing else it gives you more treasure and gear to sell from earlier missions, but also lets you run up different strategies and equipment combinations and try out new synergies. My initial party was 1 Warrior, 1 Wizard and 1 Priest, so I mainly focused on heals with the Priest. If I hadn't tried to bring up a new group, I wouldn't have seen how much damage Priests can do when they don't have to concentrate solely on party heals and how nice intersecting healing auras are.

 

IF you have the chance to pick up St. Xarol's Axe it is a great offensive weapon for priests. I lucked into one fairly early and it made chopping down little buggers much faster (not as fast as FS but I never used FS until I had beaten the main SP missions).
If you are still low on Power Tokens then the
Hefty Stout Club another rare is a nice 6 good attacks weapon for 0 tokens.