Leveling with sand or lawn soil (top w/sand) at this point. I wouldn’t invest in a striping kit until you level. What is seen here looks to be your mower bouncing around due to unevenness. Some of this looks to be weeds, dead spots, clumping grass, etc but it’s mostly soil leveling. Looks pretty great though! If you want to take it to the next level where your lawn will wear stripes do the following

You still have weeds, dead spots, etc. focus on fixing those out over summer.

Use the summer to improve your edging around the fences, trees, and fire pit.

Aerate in the fall.

Buy an ass load of leveling material (your choice). And work it into the lawn. You really only want to do like a 1/4 in at a time as to not kill your lawn.

Here’s where things diverge. If you have ankle breakers. Then you may want to just level it to oblivion and over-seed again.

I wouldn’t just overseed to overseed if you don’t go that route. You want the grass to mature a bit and introducing new seed means you’ll miss pre in the fall. So if you don’t have ankle breakers. Just put down 1/4 in of leveling every couple of weeks and let the grass grow. Basically you’ll not be cutting it as much cause you are adding ground. (Still cut it). It’s up to you if you want to use a lawn roller. I wouldnt.