HOW TO NOT "WRECK" YOUR CLASSIC
Getting into a classic car build is an exciting time as a world of possibilities lays in front of you. There are so many options for ways to build a classic car.
Do you do a factory-fresh restoration? Or create a wild custom which radically alters the car's appearance? A race-ready machine destined for hardcore performance use? Or do you build something in between, which is today known as a "restomod"? All these questions can spark our creativity into a wildfire, setting us off on flights of fancy and leading to some amazing concepts for car builds being brewed up in fertile minds.
To avoid getting in way over your head, or hating the finished product you have spent years building, take some time to consider the following before diving into an old school project car.

RESEARCH THE ERA THE CAR IS FROM
Cars are styled and engineered within an era, as they have to fit the lives and environment within the world at the time they're released. This means some cars are easier to turn into corner-carving time attack beasts as their base engineering is better. While other cars are simpler to airbag and turn into a belly-scraping custom with wild paint.
Before the late 1980s most cars rocked a carburettor (or two or three) and so these cars can be way more involved if you want to swap it over to modern EFI (or a modern engine). On the flip side it can be easier to do wild body modifications to very old (1950s and '60s) cars as the gauge of metal their bodies and frames were built out of is thicker and easier to weld.
Ultimately, understanding the era the car came from also helps you stylistically. You'll find colours, wheel ideas, graphics and countless other mods from road and race cars of that time period, which will transfer over to your car much more easily than adapting wildly different eras.

YOUNGER MODELS ARE GREAT FOR TRANSPLANTS
Old cars have a great vibe, and they're a lot of fun. Having to learn how to cold-start a high-compression carburettor-fed engine is a novelty when new, like learning to watch the coolant temperature like a hawk in traffic, or leaving acres of real estate in traffic due to old style brakes, or having to pull over to try and de-fog the inside of the windscreen in heavy rain.
But it gets old. This is why SO MANY cars end up as "restomods" with late-model engines, or late-model tech on the original engine. We all know how popular LS, Barra, Honda-K swaps are, as well as RB26s, 2JZs, SR20s and more having been swapped into countless old school cars to instantly repower them with way more power than new, better on-road manners, better fuel economy, and easier servicing.
But you don't have to swap the entire engine over. Updating an older engine with aftermarket EFI, adapting modern ignition systems to get rid of troublesome points or outdated tech, modern radiators and fans, and alloy engine components to shed weight and heat are all great ways to make an older engine drive as reliably and smoothly as a newer engine.
With some careful planning you can integrate the best of original hardware and modern tech to retain the original vibe of the car while making it work better than the manufacturer ever could imagine.

START BY KEEPING IT SIMPLE
Over-building a car is a real problem a lot of car builders - even experienced ones - fail to see until it's too late. Many of us are well-versed in dealing with scope-creep in a project (aka Project Snowball), where a job starts off as a lowering job and wheels, turns into rebushing the suspension, then changing arms, and soon you've got all-new brakes, custom wheels, chassis upgrades, an engine swap, and so it rolls on.
However, over-building a car can sneak in as you're distracted by The Snowball. Does you street cruiser and weekend sled need 1000hp? That sort of power comes with huge complications to the rest of the car, and you can't simply put a 1000hp into a classic car without huge, expensive mods to the drivetrain, brakes, cooling system, electronics, and more. And will you even like driving a 1000hp car?
Of course going fast can be fun. But keeping a classic car simple in its scope allows you to enjoy the experience of having something from that time period. A simple bodykit, simple wheels, simple engine mods and interior upgrades means you can enjoy the vibe of the car, and decide if you want to push it further later on with a more comprehensive build.

UNDERSTAND SOME PAINFUL TRUTHS
New cars are faster, easier to drive and live with, and safer than a classic car. What you get from a classic car is a mixture of emotions centred loosely around nostalgia, but they're not a panacea (a single, epic solution or remedy to solve all your problems).
They take dedication (of time and money) to work on and find solutions to problems that will pop up. They take humility as they'll probably break down at least once, or make embarrassing noises or smells when you're busy showing the car off (normally to someone you're trying to impress). They take literal blood, sweat and tears as you learn to work on them and wind up with scars from sharp edges or slipped-spanners.
You'll need to budget for tools (and somewhere secure to keep the car and tools). Insurance. Maintenance. But I can safely say, after 26 years living with a bunch of old school rides of various ages, they're always worth it. Just don't expect too much from them.

IGNORE STYLE CRITIQUES AND HAVE FUN WITH YOUR CAR
You can't go on the Internet today without some pelican-touching pesterer dishing opinions about things that don't really matter to them. These mouthy, annoying flops who engage mouth first before engaging their brain are typically MOST vocal when it comes to the subject of cars and what someone does with their own pride and joy.
We've all seen them on social media. "Wrecked a classic", "ruined", "someone needs to take that off you" are all the common ways these toilet-dwelling fart-sniffers bring down someone posting questions, or sharing pics or vids of their pride and joy. And it sucks.
Classic cars, for the most part, were just cheap old nuggets at one point. Please understand that if these sadsacks really felt as strongly as their whining, bleating posts sooking about what you've done suggest, then they'd have been out there collecting all the old cars to "save them" from people "ruining them".
But they didn't do that, because it doesn't really matter that much to them. They're just trying to bring down people who are living their best life, so the best answer to someone telling you that you wrecked your car is to keep driving it with a big, fat smile on your dial and let them suck on the hydrocarbons spilling from your exhaust.