You've both asked simple, straight forward questions in which the answers could fill books. It's like asking someone to describe the best way to raise a child. Each child is different and needs something different. How do you train your vocals? how do you become successful when starting out? both require patience and lots of practise. both also require coaching. even successful pros still coach.
what do you do if that isn't an option at the moment for whatever reason? Read out loud. a lot. and read everything: cereal boxes, toothpaste ingredients, the back of your recent xbox game, the toaster manual, your favourite newspaper, any paperback... you get where I'm going. Also, record yourself and listen back. get used to how you sound. record a lot. record anything and everything. don't be embarrassed by your mistakes, learn from them. try different vocal ranges, voices, pretend to be a trumpet or a dishwasher. but do it.
Make sure your recording space gets as much attention as your gear. the best gear in the world will not sound good in a poorly treated space. you tube is your friend here.
Is Mandy for you? tough to say. you could have a voice that everyone wants, or you might not work for six months. with any P2P (pay to play) you have to be patient. and remember, these sites do not guarantee they will get you work, only give you access to work. they are like dating sites, which you also pay for. those sites give you the opportunity to set up a date with someone. what you do at the date is up to you. same with the demos here. You can only do the best that you can and hope someone likes you, but remember you will have a lot of competition. since covid, there are more VO people than ever.
but if this is something you really want to do, you'll know it, and stick with it and you will work. this is not an instand gratification type of job.
Practice, patience and play. play around, do different things, change it up. and make sure you get an honest friend or coach to tell you if this is for you, or if you need more practise. The only way to change is to try something new. Not everything is going to work.
if you ever have any questions, feel free to hit me up during office hours. have a great week everyone. cow bella.