I started playing this when it first came out and then gradually other games took over. Looking back I see that there are plenty of new options available. I am typically the only person of my friends who spends their money on board games so if I get stuff it will be split for two people to draw from. What would you guys suggest I get to open the most options and such?

It depends on what you like. But since you already have the core set, I'd say you want Guardians of Hernfar (Daqan expansion) and Warband of Scorn (Uthuk expansion). Those will really increase your building options and give you new Legend units to choose from. I'd also suggest the dice pack. It is so much nicer having 6 dice each.

Personally, I'm not a huge fan of the reinforcement packs. I don't dislike them and I'd gladly play against someone who has them, but they don't really do it for me. You may feel otherwise. The reinforcement packs are interesting because they come with a single unit and only 3 lore cards, but they also come with scenarios that differ from the standard VP fight, so depending on what you like, you might consider that a better option than more units for the same kind of battles. Though with the Scenario editor online, I would rather just buy more faction-specific units to use in fan-made scenarios if I wanted to do something novel.

I feel like the Undead will be really popular, so if you know someone who likes that sort of thing, you may want to pass on one of the other factions' expansions in favor of picking up some Undead. For example, if I lived in the same city as my twin brother, I'd probably pass on Guardians of Hernfar and get the Undead expansions instead since he's really into Waiqar the Undying and I like the Uthuk Y'llan.

Cool. I do not know much about the lore although the undead do look awesome. Should I wait till I can get both before using them since again its only my stuff my friends will be using?

Well, it depends on how much you care about balance and how much you want to spend. If you're willing to get both Waiqar (Undead) packs and the Daqan and Uthuk expansions, you'll have a ton of content, that should hopefully be pretty balanced. (I'm assuming that the reason they're releasing two packs for Waiqar is to catch that faction up to where the other factions are with the core + expansions.) Of course, at $40 a box, you're looking at $160 to get all those expansions. If you like the idea of the Undead, you could just get one box of those to supplement with the core set. That should give you 3 factions, each with roughly the same diversity. If you get both Undead boxes, your Undead faction will have more options than the other two.

So the short answer to your question is that there's no need to get both right away. You could get one Undead pack, see how it goes, and pick the other up later. The biggest issue is that we don't know when the Undead packs will be released.

Right now the only expansions to buy are the Uthuk/Daqan army packs and the (just recently available) Razorwing reinforcement pack. That's about $95 retail on top of the core set.

The other expansions (2 Undead and 2 reinforcements) are coming in the next few months, so there's time to plan for them.