[RPG] the non-homebrew goblin with the highest CR

It really is up to you. There's nothing in the rules that'd prevent it - 4e doesn't enforce alignments. That's a departure from earlier editions, where alignments had mechanical meaning. In 4e, they are there purely for flavor and you don't need to worry about breaking something by changing them.

There's nothing in the nature of goblins that makes them evil, and even if there was you could change that as it's your world. Even in some other editions, when they say "Always Evil", that's meaningless. If that line bothers you, make up goodlins. There are, after all, good undead in D&D 3.5.

Not everything is quite as variable, though. Demons are usually beings of pure evil. Saying demons can be good has ramifications. No one cares about the goblins.

So why are goblins evil? Because that's the stereotype, and a game has to fulfill stereotypes before it can deviate from them, or at least that's the approach D&D tends to follow. In the world you describe, most would perhaps be evil because those are their cultural norms, reinforced by social injustices of others. A goblin's strive for goodness against such forces would make for a compelling story.

I'm going to address this in two ways. The first is with the resting rules as presented in the PHB/Starter, and the second is to have a short chat about the alternative resting rules as laid out in the DMG.

First and foremost, we need to talk about how resting works in 5e. Short rests have a timeframe of 1 hour, and long rests have a timeframe of 8 hours. This means that in most scenarios you only want to take short rests in dungeons, and to do so sparingly. To some degree, this is the point of the time frames being this long, dungeons are designed to drain resources from PCs so that final battles in dungeons are meaningful, at least for some value of meaningful.

However, each party is going to have their own comfort level with how many resources are expended at certain points in the dungeon and how much rest their heroes need. How much trouble they have finding a safe spot to rest (or how effective their watches are if they do take a long rest) is up to you as the DM. I can tell you that the first group of players I ran through the starter was feeling mighty uncomfortable by the time they cleared out the second or third encounter, several PCs had nearly died and it seemed like a really good spot in the adventure to take a long rest. How you adjudicate this as a DM is sort of up to you. Long rests are not completely interrupted if a fight breaks out, so it's within your rights to let your PCs rest, but to spring an encounter on them while they are sleeping (though, if you plan to do this, it doesn't hurt to let them know either implicitly or explicitly, that resting here is not safe and may end up triggering an encounter over night). If you really don't want them resting in a certain spot, let them know, they see patrols, or traces of them that seem to pass regularly, or whatever.

That said, in many dungeons, there is no reason that you can't simply let yourself out into the wilderness to go have a nap. This is a possibility in the first cave in the starter set. A 15 minute hike into the woods should reveal a reasonable camp site that won't get discovered by the goblins.

Finally, there are alternative resting rules. They basically allow you to adjust the amount of time short and long rests take in order to defray certain costs. For instance the easiest one changes short rests to 5 minutes and long rests to an hour. This is probably to extreme for your game at this time, but, just the same, it doesn't hurt to modify the time frames to get the game you want to play (these are completely laid out in DMG 267-268).

So, basically, the advise that I'll give you is decide the style of game you want, decide how hurt you want your players to be, and dictate (with some input from them to be sure) how they should be resting based on the style of game you are playing. In the starter (And this is what I've done in my 5e games, including the starter), don't be too hard on your characters for wanting to take a rest, it's not hugely consequential, and they'll probably have more fun if their toys are all available for the rest of the session.