You are describing a situation very similar to my own, but I'm practicing piano. I'm teaching myself so I think a lot about exactly what I'm doing with my practice. So I sympathize with your situation.
About perfectionism. It may be better to have a notion of objectives and goals where objectives are specific, achievable things you can check off a list as done, but goals are unobtainable points, ideals that can never be reached.
Perfect can be a goal. But perfect doesn't exist. It's an ideal you strive toward, but never reach. It's the impetus that makes us keep working. Keep that in mind and don't get hung up on it. Certainly it won't be helpful to repeat a practice pattern over and over and over until it's "perfect."
Create specific objectives to reach for whatever you work on before moving on to the next thing. There are many ways to set those objectives. Probably the simplest is time. Work on pattern X for one week, then move on. You could set a more technical, musical goal. Practice until you can play a pattern in all 12 major keys, or practice until you can play something at a certain tempo.
I think it's important to deliberately include contrasting material in practice time that differs for the main focus.
If you are working on chord based material, include something else like a scale pattern. First, it will give you some mental relief from playing too much of the same thing. But, it's also important to sort of "forget" the main material just briefly and then return to it with some freshness. I think there is a psychology of memory aspect with this where your brain needs some "inactive" time to "process" what you have been practicing. I've read recently about how a lot of memory processing happen when we sleep. It may seem like inactive time, but your brain is actually working to process recent events. You can also compare it to exam cramming. If the only way to do it is cram and exclude everything else, you haven't really learned the material. A process of leaving and returning to material is necessary to really learn.
Along similar lines I think it's nice to have a stock set of pattern to play all the time or that you bring back with regularity. It gives you a break from the current material and keeps you solid on fundamentals. For example I try to include classical cadences in all keys for most of my sessions. From time to time I bring back finger independence exercises.
Work on things that are not familiar. This gets back to the notion of perfectionism. Little is gain by spending time with what you know. You have to constantly seek out the things you don't know. This will expand your horizons and challenge you to adapt. Trying to "perfect" one thing won't really take you to anywhere new.
Try to take a new approach with the familiar so you can expand the knowledge you already have. A lot can be done with familiar patterns by changing up the basic musical parameters. Change ascending patterns to descending. Change the meter - usually you can do this by with small rhythm adjustments. If a rhythm is even, change it to uneven, dotted rhythm. Change block chords to broken chords. A personal favorite is to take a practice pattern and then elaborate on it to make a 4 to 8 bar phrase. You can go on and on with how to vary material. The point is to focus on the creative aspect of varying familiar ideas rather than perfectionism.
...when to add new material..?
- My basic objective is to have two practice sessions every day, once before I go to work, and again when I come home. Each session is about 30-60 minutes. I make up all my patterns on my own.
- I typically change up the principle pattern about once per week, but I never really play the exact pattern every single day. I'm always doing some small variation. But I deliberately change the principle material roughly each week.
- I try to set an over arching goal that will require a few months to complete. For example, I identified meter and counting as a weak point to improve. I realized a whole series of exercises will be necessary to work on these skill: playing to a metronome, counting aloud, tempo changes, various rhythms and meters, changing hands and using a variety of musical figures. I don't work out all those details all at once in the beginning, but have some notion of how big the endeavor will be and I mentally block out a period of months that needs to be devoted to the pursuit.
Each person will approach things differently, because they will have different goals. But this gives you an idea of my approach and how I think about changing material on daily, weekly, and monthly levels.