Firstly let´s tackle the calorie and protein issues. I can tell you with 100% certainty that it is easy to consume 3000 calories and adequate protein on a plant based diet. Meat is a protein which is 4 calories per gram. All carbs are 4 calories per gram and then fats are 9 calories per gram. On a plant based diet if you are consuming lots of grains and legumes you are getting lots of carbohydrates and proteins in them all as each food contains a ratio of both vs meat which is just protein. These foods are more complete foods. So consume lots of rice, potatoes, pasta, buckwheat, barley, lentils, chickpeas, nuts, beans etc Also then you have fruits which are a carb and can have loads of smoothies to up your calorie intake. Also good fats like avocados, nuts and nut butters are an easy way to get your calories in.
So it is easy get your calories in. One thing I must stress though is that I am not a believer in counting calories. It is not a realistic way to live longterm and I only believe in following strategies you will follow longterm. Are you really going to count calories forever? There is no need. Your body and results will show you how good your nutrition is so just tweak things a little as you need to.
Next in terms of difficulty adopting a plant based lifestyle I see it that there are 2 types of people – 1 those who can go cold turkey and completely transform habits with a decision and 2. the majority of people who are better to gradually improve over time and create lifelong habits in so doing. So you alone know what type of person you are so plan your strategy around it. Personally i always feel it is better to focus on creating positive habits and to keep making weekly changes. It took me 7 years to finally go 100% plant based!! There is nothing wrong with it taking time once you are moving the right direction and educating yourself and growing your awareness of the truth.
So the most important lesson from this question is that a plant based lifestyle will provide adequate calories and protein once you are consuming a diet with a wide variety of grains, legumes, fruit and greens. And make sure to consume good fat sources as well. And also in adopting a plant based lifestyle go at your own pace. Just make sure you are always makng positive changes.