I have written four poems and will keep writing more. How many should I put under one collection, and around how many pages should it be? Any ideas on how I should go about the self publication process? I'm totally new to this whole system, it'll be my first publication.
The typical format for small, personal poetry collections is the chapbook. You can actually put one together yourself, it's really just several sheets of letter paper folded in half with a cover made of heavier stock. If you do a poem a page, you can handle somewhere between 12 and 24 poems in this format.
It's definitely the lowest cost option for self-publishing, and has a long history and good reputation in the poetry community. Since most publishers don't handle poetry, and the market for poetry is limited, there's less stigma around self-publishing in the poetry community than elsewhere. There are even legitimate competitions for poetry chapbooks.
You should probably expect all your sales to be from books you sell personally after doing a reading somewhere. It's very unlikely that people will purchase any poetry book from an unknown writer without a personal connection.
One of the easiest ways to self-publish your poems would be to use Kindle Direct Publishing to sell them as an e-book. You can create an e-book with as few or as many poems as you like, and Amazon provides the platform for selling them. You do whatever you can to promote them and let people know about them to try to garner sales, which isn't going to be all that easy itself, but at least you don't have to worry about how to go about making them available or collecting the money or distributing them to your potential buyers.
If you want to provide a print version, then the number of poems will become a factor for you. I personally would recommend using CreateSpace (another Amazon property) because it is very inexpensive and again provides you with an immediate sales platform. One of the things you will need to keep in mind is that CreateSpace will not print a book with less than 24 pages in total. One of those pages can be a title page, another can be a copyright notice page, and you could use yet another for acknowledgements. You could also throw in a blank page or two at the beginning or end if you like, but your total page count will need to be 24 pages. That would mean that you would most likely end up needing at least 16 pages of printed material in order to get them to publish your book, so you should shoot for at least 16 poems as a minimum if you choose to go with them. One disadvantage of printing a smaller book like this is that you won't be able to get your book title or your name on the spine because there just isn't enough room. In fact, each of my books with 100 poems has this same problem. Even with that many poems, there isn't enough space on the spine for them to print anything.
One of the great advantages of CreateSpace is that they have a very easy to use cover designer that is free of charge, so you can use it to create your cover. I actually created my print versions first and then used the covers that I created through their tool as the covers for my e-books.
I have published six volumes of poetry with 100 poems in each, as well as two separate collections with 450 poems in each. I was fortunate to have already developed a very large catalog of poems, so deciding on a number was easy for me. As someone who is just starting to develop a body of work, you will want to take an approach that works best for you.
I can't really advise you on how many poems you need. This is determined by your purpose, audience and how many you can produce.
I can tell you that if you plan out your publication so that it only has to be printed and bound that will be a lot cheaper than if you just present the text to be printed. For example, my wife and I produced a charity poetry anthology of about sixty pages. We sent the pdf and colour cover to the printer and it only cost about £2 per copy for a pretty small print run.
Who is your audience and are you expecting to sell your copies or give them away? How big do you want the print run to be? These things affect how you publish.