Mario Kart 8 Deluxe – How to Unlock Gold Mario

As the other answers have stated kart information is available in the game itself. Press +/- to bring up an info panel while selecting your kart parts to see these stats. As you switch kart parts the game shows how these changes affect your stats. I've added a picture below to illustrate the view I'm talking about.

Edit:

Thanks to @Grirg for linking me to an updated Mario Kart 8 Deluxe wiki page that includes both kart part stats and racer stats. Due to the amount of kart parts available in MK8D you'll have to go to link for that information. Some kart part stats are available in game but it only shows their overall affect on your kart not the individual part as well as missing some of the other stats available on the wiki. I've included the updated character chart below and as I stated before when it comes to the characters you chose there doesn't seem to be any information available in game or if there is I haven't seen it.

Based on this article written about these two features, it looks like this is how they work:

The auto-accelerate feature seems made for newcomers only, or for those with serious conditions requiring them to use it. A big part of the Mario Kart experience is timing those button presses just right to get the starting bell boost. Letting go of the button to brake can also be used as a strategic play. In short, acceleration is one of the ways that players can exert their control in the game. To give that up seems, at first, unthinkable.

From this, it looks like the game accelerates for you so you don't have to hold down the acceleration button the entire time. However, it prevents you from not accelerating, which is useful strategically.

The smart-steering feature seems to work like this:

Smart steering works in reverse: It guides players’ karts so that they remain on the road at all times, turning them when they need to turn. Smart steering also makes all of the game’s skillful shortcuts inaccessible. It’s a useful option for those in need of additional help with the joysticks.

This prevents you from going off-road, but it also appears to prevent the player from going on shortcuts.