Call me an over-enthusiast but presently, the highest priority in my life is to achieve the object of Nirvana or moksha.
This is good! You need enthusiasm to stay motivated in your practice.You also have a sense of urgency which will help you progress.
By performing Vipassana, I want to achieve Nirvana and in this lifetime only. I'm prepared to do anything for it, even leave my current profession and staying as a monk if required.
You can not realise Nibbanna by willing it to happen,you have to create the necessary conditions.Take all the willing( will power,effort,urgency and determination) and apply it to the right spot which is creating the conditions.For example instead of exhausting all your energy on "I have to attain Nirvana in this lifetime",you can say "I have to sit and meditate for 10 minutes today".Because without the journey there is no goal.So make the journey your goal.
Also don't stop thinking/wishing/contemplating Nibbanna.Practicing the Dharma isn't like wandering aimlessly without a goal.Thinking everything is empty so there's no use doing anything.Or not having a goal.This is something you do after you've realised nibbanna not before.You might not know what Nibbanna is but you know it's not suffering like your experiencing now.So thats a good way to motivate yourself.It's also a good way to keep your mind fixed on the other shore Nibbanna.
Let the results arise on it's own.Don't place your effort on the result.Just like when you plant something.You put your effort on watering the plant.Not making it grow.It will grow on it's own.
Trouble is, I just don't understand how exactly to go about meditation. I've read a few suttas but I just don't understand what to do while doing Vipassana meditation. In a 10-day Vipassana course I'd undergone, I'd done Anapana (breathfulness meditation) by keeping my mind on the entry and exit of breath at the nostrils. I've done this for several hours and I still do it sometimes.
Keeping the mind on the entry and exit of breath at the nostril is Samatha Meditation.You do this to calm the mind.Achieve samadhi. It's a tranquility meditation.This should be done before practicing vipassanna.Your not observing anything.Your just staying with the breath.Anything that arises you ignore and return to the breath.Try doing this for a few years first.Whatever suits you.Samadhi is like a steady hand.It's aim is to develop concentration so that you can hold your mind steady on something as slippery,rapid and subtle as thoughts,intentions,feelings,etc(Vippassanna Practice).Samatha can also give the mind a good home or resting place.So something you should be practicing for the rest of your life.
I also do mindfulness meditation sittings (by observing my thoughts impartially) for at least an hour in one sitting daily.
Mindfulness Meditation is like when you sit and do Samatha Meditation.Except this time you don't ignore your thoughts,feelings,intention,sensation etc and return to the breath.You stay with it.Observing it.But when you feel like it's slipping or too painful,powerful, go back to the breath.The breath is your anchor.
Now, all these practices are great and take me into a calm and tranquil state of mind. But I don't seem to be getting anywhere towards my ultimate goal of Nirvana.
Realising Nibbanna is not all about meditation.That's why it's not called The One Noble Path.But the Eight Noble Path.It is holistic.It requires every aspect of your life.The Eight Noble Path.You must put the same amount of effort you put on your meditation on your sila.
Is there any way to know how long is it going to take me with this speed, or how do I increase the speed?
No.There's no sure way of knowing.It would depend on one's karma and paramis.But no effort you put in is wasted.
Most importantly, Is joining the sangha and practicing full-time monkhood the only way to achieve Nirvana?
No it's not the Only way. You can realise Nibbanna as a lay person.But monastics have a the advantage of living in an environment that's conducive to their practice.