Overview:
-Estimated achievement difficulty: 4/10
-Offline: 49 (1000)
-Online: 0
-Approximate amount of time to 1000: 30-50 Hours
-Minimum number of playthroughs needed: 1
-Number of missable achievements: None!
-Do cheat codes disable achievements?: No Cheats
-Does difficulty affect achievements?: Only 3 (See Introduction)
-Glitchy achievements: None
-Unobtainable achievements: None
-Extra equipment needed?: Drum, Guitar, and Microphone Peripherals

Introduction
Welcome to the Road Map for Lego Rock Band! This is by far the easiest Rock Band game to achieve the full 1000 in. There are only three achievements for which you will need to play on Expert: Brian MAY Be Jealous, The Final Countdown, and Solid Gold, Easy Action!. All of the remaining achievements can be obtained through Super Easy difficulty and the fan trick, which makes this a breeze.

Step 1: Story Mode
This is where you'll get the majority of the achievements. Simply go through the story mode until the end, playing on whatever difficulty you feel comfortable with. By the end, you'll have all the vehicle and rock power challenge achievements, as well as New to the Scene, Twinkle, Twinkle, Pencil Pusher, Local Legend, and Universal Acclaim.

Step 2: Shopping
Now that you've accumulated your riches from Story Mode, go to your rock den and purchase items for the walls, floor, ceiling, etc. until you get Hovel, Sweet Hovel, House Proud, and Luxury Living.
Afterward, go to the Rock Shop and buy clothes and instruments until you get Bare Essentials, Appetite for Apparel, Fashion Victim, Gear Head, and Instrumental.
Now, the final part of this is to go into the office, go to the left, and hire all the entourage members. Doing so will get you You're Hired!, and #1 Boss. If you don't have enough money to complete this step, just come back after the next step.

Step 3: Tour Mop-Up
Now, go back and complete every single gig in Story Mode for Veteran Performer. It'll take a while, so if you get bored, use the fan trick (use vocals on Super Easy, put the mic in front of a fan or something that constantly produces noise and you're guaranteed to get 100% every time). Afterward, if you don't have 1000 stars and 1,000,000 fans, go back and use the fan trick to gain more stars/fans until Super Stars and Fan-TASTIC unlock. If you haven't already, also get Stud Farmer. In getting Veteran Performer, you'll also get Tour de Force, Long Distance Runner, and Endless Shameless (If you have trouble with endurance for the latter two, refer to the fan trick).

Step 4: Multiplayer
Now you get to do the multiplayer achievements. All Four One! and Practice Makes Perfect require 4 players, but technically you could do both of these by yourself if you have 2 guitars, a drum set, and a mic (see Spade422's thread here for help on doing Practice Makes Perfect by yourself, and in doing so, you'll also get All Four One!), but it is a lot easier with 4 people. Just refer to the guide below.

Step 5:Flawless Achievements
Now go for the flawless achievements. They require you to get 100% on a song with an instrument, but don't specify a difficulty or song, so just set it on Super Easy on "We Will Rock You" and they should be painless.

Step 6: The Final Step
There are only three achievements left. Unfortunately, they're the hardest ones. First, go for Solid Gold, Easy Action!. The guide below specifies the easiest way, but if you don't have access to Xbox LIVE, try Expert Bass or Drums (whichever you're better at) on "We Will Rock You."
Next, go for Brian MAY Be Jealous. To get this, you have to get 100% on a guitar solo on Expert. See the guide below for some easy solos.
Finally, the achievement that separates the men from the boys. The Final Countdown. It's without doubt the hardest achievement, so you'll need to go into practice. Aside from that, I can't give you any advice that will help; it's all about skill. Good luck!

Conclusion
You now have 1000 in Lego: Rock Band, and you can now officially say you got the full Gamerscore in a Rock Band game. Congratulations!