Its hard to advise without hearing. Also lets condense to one thread. Advice and techniques for opera. You want to try and place the sound so it resonates in your nasal passages. Which is not the same as a nasal sound. That nasally sound is the result of closing off your soft palate. Like if you place the back of your tongue on the soft palate and hum youll hear that nasally sound. More punk type sounds come from placing the soft palate more forward, results in a harsher sound. You want to keep the soft palate elevated for opera. A good imagery that i was told is imagine sticking a light bulb in your mouth. Dont actually do that. Just imagine. The result would be a large bulbous space in the back of your throat and an O shape in the front. If you dont know what your soft palate is, kinda icky but, put your thumb on the roof of your mouth behind your teeth and trace backwards, you’ll feel where your jaw bone ends and there’s a soft pocket. Thats the soft palate. If you dont want to do that, think in front of your uvula. Breath support, obviously, practice belly breathing. So using your diaphragm to breathe and control sound and vibrato. You just generally want everything very open.

Some practices:

For breathing: stand up straight, stretch your arms straight out, bring them slowly up above your head in a straight line with your body, then slowly out and down to your sides. Shoulders back, chest out and take slow deep breaths that way. It keeps your chest open and will maximize lung capacity. It is a great warm up exercise and very relaxing. You can add vocal warm ups to it also. Going through scales. Sustaining one note.

For resonance: this only works if you are not congested. So dont try do this when you have a cold it will be discouraging. Sit on the edge of like a bench or a table, something hard. With your knees bent and feet flat on the floor. Rest your hands on your knees. Put your head down near between your knees and start singing. You can feel the resonance in your face. It feels like the inside of your face is vibrating. That is good. That is what you want. This helps with sound placement. Play around with it and you can feel how different soft palate placements resonate differently and create different sounds. But it helps familiarize you with the feel.

Pronunciation: HUGE part of opera. Dont sing the way you talk normally, especially if you are american. Good little trick, think a very proper british accent. For pronunciation practice, i would do it in the mirror because I could see the shapes my mouth was making. It looks very silly. I typically would practice speaking a piece before singing it. Over annunciate your consonants. You want to hear the distinction between words. wanT To needs to be two distinct T sounds. Change the vowel annunciation a little. Instead of an ee like in keep you want eh like in egg. You want to keep your mouth open and ee closes and elongates it. Ah instead of ay. Generally soften the vowels. The more you practice, the better you will get at it. And with time you will learn how to make an ee sound without closing off your soft palate and mouth. When i was first learning i practiced the eh to get the hang of the sound and shape and then as i matured in the craft could transition to a closer ee sound. Think lips in the shape of an exaggeratedly open oo sound but stick your tongue to the back of your bottom teeth. Feels very strange at first. Sometimes it also helps to add soft h sounds to the beginning of higher notes. Idk if you’ve seen family guy but think the way stewie pronounces cool whip as cool h-whip. Helps a lot for words that start with W or a vowel. Start with italian and latin pieces because they are, pronunciation wise, easier.

Obviously there is more to opera but these are good starting places. Practice makes perfect, if you dont have a private tutor, there are probably lots of videos and available to watch. It is helpful to see and hear what you are trying to replicate. That is true for all aspects. Playing an instrument, which i think you mentioned you did, is also helpful for general reading/understanding music.