I am a beginner, I sing along while playing some chords and scales in the guitar. I am considering to use a vocal effect to make practising more interesting and fun. I prefer to try different things and timbres adding more interest to the sound. Do you think this kind of "camouflage" is something to avoid?
Untrained voice tends to have all sort of problems. Onset, pitch, breath control, stability, connectedness: that's all stuff that easily gets masked or muddled with effects and you want to work on all that. And the first step to working on it is to work on one's awareness. If you are muddling your voice right from the start in order to avoid being aware of the scope and kind of your problems, this may make practice more enjoyable for you, but not performance for your listeners.
And you ultimately want to get somewhere with practice. "Exercises sound like not good music": they aren't supposed to sound like good music. They are supposed to let you work on your vocal production systematically and realistically: if they sound bad, it's usually because you still have work to do.
Basically you say that your voice is bad, but you have some music that you like. So you feel good about your singing because of your choice of music, and you want to avoid having to hear too many details of your voice by using sound effects, and then enjoy singing practice in that way.
That sounds like you are preparing for singing under the shower. With lots of water noise and no audience but yourself. Make no mistake: that's fun. But not exactly what "practice" is usually supposed to prepare you for.
Reserve the fun part for the last quarter of a practice session.
When recording, it's common practice to add a bit of reverb to a singer's monitors. So why not when practicing, if it makes it more enjoyable? Be aware though that NO-ONE likes the sound of their own voice, and sound engineers are used to vocalists asking for ridiculous amounts of reverb and other effects.
All you other questions merely illustrate the futility of self-instruction. Yes - join a choir. Yes - take lessons. Exercises are just that, exercises. They are designed to improve your technique, not to be enjoyable music - though you should be able to enjoy the improved control, sound and range that they bring.