total newby lost in the setting

Yes, dire foes are legal
If you have also someone who is interested the 2 player packs are a good deal and a good start for a vanilla army. But if you can’t find anyone to split with then a faction box is a good deal.
There is also the 3rd and more expensive option of buying stuff that you like and continue building from there.

:edit:

By faction starter I thought you meant the sectorial “army packs” like the Corregidor one which are 300points. If you meant just the simple starter packs, then yes they are the basic stuff you can buy to start the faction you like.

 

Look at the minies you like and check out the lore of each faction before you decide.

I recommend picking a faction or sectorial starter.

 

Dire Foes are just extra named characters and are perfectly legal for play. There's none of this "opponent's permission to use special characters" in this game.

The full rules are available from the corvus belli site under "downloads" usually. They are the same rules as in the rulebook(s). As are templates and marker sheets to print out yourself.
The rules work with all factions. They all tend to use common weapons. A given weapon from one faction will have the same profile across factions.

For the background on units and armies, it's mostly in the rulebook sets (but there IS some available on the Human Sphere page https://human-sphere.com/index.php?title=Main_Page that will probably help your selections.

 

Pretty much anything you can construct with official army builder is legal (unless builder tells you otherwise). Make sure that you have options set correctly for your upcoming match though (mercs on/off, correct point limit etc.).

As for what's better to buy: it may be a discouraging answer, but you might want to find out what you need and plan your purchases accordingly. One way is to look at minis and figure out if you like them visually. Another way is to go to faction forums and ask people stuff along the lines of "I'm going to start this or that army, what is a good place to start?".

It's hard to answer generic questions like that without mentioning particular product because not everything is equal here. For example, for a while we had (and you can still maybe find one) 300 pts sets for different armies. Some of them were pretty on point (so I heard almost everything in Tohaa 300 pts box is of great gameplay value), others not so much (may be not the best example, but 50% of Corregidor 300 pts box was questionable).

Then there's another thing that could matter, which is your current aim. Say, if you intend to have something playable in low very point games while you are expanding your collection, some sets are better than others. For example, Hassassin Bahram starters are traditionally high-to-top tier in terms of value, but only so if you intend to make enough purchases to be able to field several configurations of 300 pts lists (so, most of the time); others have starters that are more playable in low-point training games (100 pts or so; although Infinity is not built around such small scales, so you are definitely going to upscale; but we're talking training games).

 

As a fellow noob playing the game for a couple of months now, I would like to make a suggestion.
If you do not go for a split Red Veil or Operation Icestorm box with a friend, carefully plan and research your purchase.
A popular reply here whenever someone asks what he should start with is 'just buy whatever models you like'.
I do not think this is the best advice. I bought into the faction I liked the look of (Morat Aggression Force, which is a sectorial from the Combined Army) and while I do not regret it, the faction is considered underpowered and it provides a rather steep learning curve. It lacks many tricks and cool toys that other armies have at disposal and while its troops are fairly versatile, they pale in comparison with other armies' top choices.

On top of that, Infinity is a difficult game and choosing a non-noob friendly faction might result in an overwhelming and disencouraging first experience.

Hope that the above did not sound too doom and gloomy- Infinity is an awesome and complex game and the community is the best I have ever experienced.
Good luck!

 

One notable exception is the generic Spec-Ops (the one you build with XP). It's only playable in modes which allow it (so basically if agreed upon beforehand) and otherwise is a generic proxy for whatever model you're missing.

 

You might feel like i´ts underpowered. But it is not. As many other sectorials it is tailored to a certain intent/mission/purpose. You can always branch out of your sectorial to upgrade your tool box.
Starting with a sectorial also makes it easier, because it doesn´t have all of the tricks. You can focus on a smaller rule set and embrace the rest later on.

Btw, All factions/sectorials have a steep learning curve. There is no easy way. There might be harder or easier factions to master, but every single one of them has to learn a lot. Nevertheless, it´s quite rewarding after a few month.

@Dfspawn you should read upon the factions and what they prefere to do. Think about which faction ressonates with you. Do you like rebells? Aliens? Heavy Armored Badasses?
After that you should try to find a club or warcore in your area. They provide usefull tips and help a lot

 

I'll take issue with a statement here.

There are no "noob friendly" forces in the game.

Every rule that exists works identically in every force in which it is encountered. So if the force that you pick can do more "stuff" then they will have more rules. More rules makes it more complex and takes longer to absorb, because there is more "stuff" to learn. THEN you have to learn how to make your "stuff" work against your opponent(s) "stuff" that you may never even have heard about. You can control your information overload though.

Start small. Learn what you have. Then expand. Based on what you feel you need. ([i[feel free to proxy to test things out[/i])

"We" don't know what kind of table you have, your regular opponents, or what the heck they like to use. That's a lot of uncertainty to work around.

Come to the forums (or Facebook, or wherever you like to chit chat) with a specific question, an identified problem.
"I really have a problem with my opponent's Croc Man multi-sniper. That guy just rules and shoots the crap out of me."

Many solutions will just require you to play differently, some will suggest specific technology to assist, some may identify an error in how you play a rule. NOW you consider what to get to expand your options and counter tactical issues you encounter.

 

If you like the Tohaa box you might want to pick it up soon. It is no longer being produced. Some will try to turn you away from Tohaa because they are "hard". They are not. It's the army I started out with. They do have tricks that no other army have, but if you have questions just ask in the Tohaa section. We are very friendly and happy to help.

I found that diving into Tohaa allowed me to quickly get the entire army due to the limited amount of releases. Because of the limited releases I was able to branch out and get the IceStorm box and start building a Nomad army and a small Pano army.