I have started with the single player on Steam but I will play online for sure.
You should, it's a pretty small but rather close knit community...with the occasional typical online bro being dumb in chat at times.
If you don't feel like grinding out single player mode to unlock all the vehicles there is a mod on the workshop that will unlock all but the DLC and Tournament store cars available called I Want It All. I found career mode to be okay though.
Few pointers if you like, obviously play as you prefer but these may help a little as some of the mechanics in game aren't well defined or explained.
Turn traction control off in the difficulty setting if you want to be able to drift through a corner without the car suddenly biting and going nose first into the inside wall. With rear wheel drive cars (which are most) setting tuning to Locked Diff and Full Rear Brake Bias tends to be the meta for most the better players and will help with said drifting through corners.
Manual + Clutch is absurdly broken if you use a controller and configure it on the right hand stick as well, and allows to be faster and more control over Auto or just straight manual. Bind shift up to right stick up, shift down to right stick down, clutch to left on right stick. Set clutch saturation to 5-10% in advanced controller options, then just hit right stick diagonally up left/diagonally down left to clutch and shift at once together.
Also if using controller set throttle saturation to 100% if you're using a trigger for it, by default it's set to 60, bumping it up to proper 100 will allow for finer throttle control.
Don't trust the armor stat either, that's not how strong you are against being hit (it does make a small difference, buit not as much as the stat would have you believe. each car has their own hit points set...some squishier than others. Some are solid front and back and squishy sides - a fully armored Roadcutter will only take 5 damage full speed head on into anything, but will crumple with a side hit even full armor for instance) but rather how strong you are in hitting other vehicles as it re-enforces the deformation sphere model of the vehicle against player initiated impacts.
More weight = heavier hit, weight is not distributed as you'd think either. Adding a heavy bumper to front of car doesn't weigh the front down when in the air for example, it's all just center of mass addition.