Hi Danny. Firstly some great work done there, like the illustration work. to answer your questions.
When it comes to charging for work, clients can differ in how they want to pay. Some ask for a flat rate fee straight away where as if others ask for just a quote it would be best to charge by hour. The best way to quote really would be to work out how long it would take you on an average but go slightly over the top in case. In terms of how much really depends on your experience and how good your portfolio is. Think about how much you would like to be earning per year then work our your hourly rate from that, think realistically though.
When it comes to asking for the money most designers tend to ask for 50% upfront to cover costs, others may ask for the whole lot up front, but it's up to you with what you feel most comfortable. If for some reason you do allow them to pay after the job is done then keep a tab on them, put a payment due by date on the job and make it clear in the invoice. If the due date comes and they still haven't paid then follow up with a reminder email.
The best way to get yourself out there is to check out sites such as behance which I see you have already done, and others like carbonmade and even deviantART as you work with illustration. You can find work through many freelance websites, one of the best ones being peopleperhour. Try to market yourself online and offline, e.g. get some business cards sorted out, brand yourself, get online and network, get yourself a personal portfolio website and perhaps invest in a bit of SEO, or learn it yourself as many others do.
Designing in your spare time is great, practice makes perfect as they say and use this to build up your portfolio. When it comes to your portfolio it's not the quantity that matters, it's the quality. Try and have 10-15 solid pieces of work in there and regularly update it and after a while get rid of any work that doesn't seem to hit the grade like the others. Lastly make sure your work is consistent, don't put very different styles in one portfolio, if you are quite versatile, which is very good as many of us are, try and divide your portfolio into clear categories, for an online version you can do this with separate pages. When you come to meet with a client, sort your portfolio into what is relevant to them, don't take anything that won't mean anything.
Other than all that your work seems to be on the right path, but what I will say more than anything is be prepared for every situation, you will learn more in the next year than you will have learned throughout uni.
Good Luck