This has been a very hard lesson for a cheapskate like me to learn: Stop using the rattle can before it's empty. Also, replace the cap if you see the slightest hint of splatter. Test the new cap on scrap before using.

With regard to the first question about the two different textures, two things: (1) Yes, you need to let it build up, and (2) don't sand back. You are just scuff sanding, that is, you are not really trying to take finish off, you are just making the surface a little rougher to allow the new coat to grip. Depending on the finish, it may not even really be necessary to scuff sand. If the finish is a kind of lacquer it may adhere to the previous coat by dissolving the top of the underlying coat. You may want to experiment or check out the experiments of others on Youtube with your particular type of finish.

With regard to drips. First, don't do anything about them until they are completely dry. If you break the surface of a bubble or drip and it is still wet, wait. There are a variety of approaches to getting rid of them. Two approaches that I have seen and tried are the use of drywall compound to build up around the edges of the drip. The idea is that as you sand down you'll be sanding the drip and drywall compound rather than drip and thin finish around it.

Another technique I have used is to scrape with a razor blade with a piece of cellophane tape on each side, and a space just big enough for the drip. That only works on very flat surfaces, however. Plenty of Youtube on both approaches.

A technique that I have used with some success, but have not seen on the internet is to take a piece of 220-320 and hold it so that the surface is convex. I then sand the top of the high spot with the top of the convex surface. I try not to push the sandpaper into the surface hard enough for the sandpaper to do more than flatten a little.

My current approach has been to address a drip somewhat as I am putting the finish on, but not to try to get it perfect. Get it a bit flatter, and take care of any bubbles or dust specs, but if it finishes clear, just keep building up finish. This is partly because I use a slow curing water based finish, and waiting to fix every imperfection would be impractical. It's also partly because it is MUCH easier to take an imperfection out wen there is a high degree of finish built up, than to do it when there is relatively little finish built up.

As in all things, YMMV, and it's good to practice. I have often made drips on test pieces so that I can practice getting rid of them.