Well first off, welcome to the Throngs! You have joined undoubtly the mightiest of all peoples and kingdoms!
To start off with your original questions, the Battalions are absolutely excellent deals! Probably one of the best amongst all the box sets. As for a Hero or Lord, you can just convert one or two models, or get a couple offline. One conversion I use for Hammerers that works well, and really, one of the only ones that is simple and good.Is taking the Great Weapon axes and clippimg off the heads, then just gluing on the hammers of the Hand Weapons, not the best. But certainly cheaper, easier and good looking.
Anyway! As for Thunderers and Quarrellers. The Thunderers are the Handgunner units. They are excellent at taking out any kind of infantry especially heavily armored ones. They work best in units of 10-18.As for Quarrellers, they are the Crossbowers of the army. These are one of my favorite units, they are excellent at range and when given Great Weapons, can hold their own in combat. Aside from being more versatile, they are also markedly cheaper than Thunderers. However excellent, Thunderers are still a good choice, and taking a small unit can always be good for support.
Now, regarding the army as a whole. In my opinion, it is one of the best of this edition. The best War Machines, best anti-magic, and some of the best heavy infantry, all combine to equal a tough and hard hitting army. Sadly though, being an older book and army, much of it is, not as usable so to say. The best way to run an army is big blocks of 25-40 Warriors with Great Weapons, and blocks of 25-30 Hammerers. Then some Runed War Machines and ranged units. Though there really are plenty of ways to make a competitive army.
Always take a Battle Standard Bearer! They will always be of use, and I always take full commands in my units in addition to the
BSB.
One thing I absolutely love of the Dwarf army, are the Runes. Some are better than others, and some, you shouldnt really use at all. But the are just unique and awesome. You should focus on defensive Runes for just about all your Lords and Heroes, though offensive builds can be made to great affect. Runes like: MRoGromril, RoSpite, RoStone are all excellent. Also RoCleaving, RoSnorriSpanglehelm, and RoChallenge are bery useful. They can be expensive, but if you set it up just right, you will cover all the necessary areas and make a damn good Runic combination.
Examples:
Thane, make hime the
BSB, give him RoCleaving RoStone and RoChallege
Runepriest, MRoBallance, RoStone, RoSpellbreaking
Runelord, MRoBallance, MRoGromril(or RoStone), RoSpellbreaking x2
Lord, MRoGromril, Shieldbearers, RoCleaving
There are just some random examples. Though there are better builds. And much worse ones
Warriors: 25-40
GW
Hammerers: 25-30
Longbeards:25-30(would reccomend against these sadly)
Ironbreaker:25-40(would also reccomend against these sadly)
Quarrellers: 10-20
GW
Thunderers: 10-20
GW
All with Full Commands of course. Other units are rather debatable, but I hope this all helps!