“What happens if I break a restriction by mistake without lifting it first?”
Technically you fail the challenge. However, small goofs won’t cause you to fail as long as you fix them immediately. For example, if you move a couch before lifting the athletic restriction, you can just move it back to exactly where it used to be when you realize your error and not fail. If you goof and forget to pay protection money, just pay it as soon as you realize. If a Sim autonomously does something that breaks a restriction (like playing games on the computer before you unlock science) just cancel their action as soon as you notice it. You won’t fail the challenge just because of that. Knowingly breaking an unlifted restriction (giving up) will cause you to fail the challenge.
“Do you have any suggestions as to which restriction I lift first?”
I have my personal favorite, but I don’t want to say. The first two restrictions lifted (one by the founder, one by their spouse) have the largest implications. I’m curious to see what unique pairs of restrictions people decide to lift first to make the 2nd generation easier. All I can advise is that you look into what each restriction is really doing to you and decide which ones hamper your play style the most.
“What happens if I receive an item from a date or outing that is still restricted?”
You may keep the item, but you may not use it. You may sell it if you have lifted the business restrictions. You may put it into inventory if you have room.
“My sim has already hit the top of a career field? Does that mean they are not allowed to go to another career?”
Your sim can go to another career field, and even reach the top of it. However since they already lifted one restriction, reaching the top of a 2nd career path will not unlock its restriction. That doesn’t mean they can’t reach and stay at the top to earn the family money. Just remember that, unless the Slacker restriction has been lifted, Sims cannot return to their old careers.
“What if my system can’t handle a 64x64 lot?”
Move your Sims to whatever size lot your system can handle and use the family funds cheat to reduce their money to 1800 Simoleons.
“What if I lift a restriction on an item when another restriction still says I can’t use it. Can I use the item?”
Unless a restriction specifically says you can use an item, even if other restrictions are in place, you must lift all the restrictions on an item to use it. For example, the Science restriction says you cannot use anything from the electronics tab. The Smoke Alarm is in this tab, and thus restricted by Science. The Law Enforcement restriction also says you cannot buy or use smoke alarms. If you lift the Science restriction, but not Law enforcement, you are allowed to use electronic items but the Law Enforcement restriction still restricts the Smoke Alarm. If you lift the Law enforcement restriction, but not Science, you may use the Smoke Alarm. The text of the Law Enforcement restriction specifically says you may use the Smoke Alarm, even if it is still restricted by others. The same goes for actions. While lifting the military restriction will allow you to invite anybody over, even for parties, you still have to lift the Show Business restriction to have parties at all.