SharePoint 2013 online can I set other column values when uploading a file using REST?

The below Javascript works perfectly when i'm trying to upload a file to SharePoint 2013 online. However I have been looking unsuccessfully for a way to populate another column in the document library at the same time as my file is uploaded. For example a single line of text column with the name "doctype". Everything that I try just doesn't seem compatiable with my code. Is it possible at all?

Here is my code:

jQuery(document).ready(function () {
$(".uploadFile").click(function () {
    fileID = $('#fileInput').attr('id');
    var selectedDocCat = $('#ddlCategory').val();
    var selectedDocType = $('#ddlType').val();
    document.getElementById("displayName").value = mainFolderUrlVal + "-" + 
selectedDocCat + '-' + selectedDocType;
    fileName = $('#displayName').val();
    var fileUploading = document.getElementById('fileInput');
    if (fileUploading.files.length === 0) {
        alert("Select a file and specify a filename!");
        return;
    }
    var parts = fileUploading.value.split("\\");
    var filename = parts[parts.length - 1];
    docTitle = parts[parts.length - 1];
    var fileExt = filename.split('.').pop();
    var file = fileUploading.files[0];
    newFileName = fileName + "." + fileExt;
    console.log('filename is: ' + filename);
    docCat = selectedDocCat;
    uploadItems(docCat);
});
});

function uploadItems(docUplCat) {
var getArrayBuffer = getFileBuffer();
getArrayBuffer.done(function (arrayBuffer) {
    var serverRelativeUrlToFolder = 'Files/' + mainFolderUrlVal + "/" + 
docUplCat;
    var siteUrl = _spPageContextInfo.webAbsoluteUrl;
    var docLibraryEndpoint = siteUrl + 
"/_api/web/getfolderbyserverrelativeurl('" + serverRelativeUrlToFolder + 
"')/files/add(overwrite=true,url='" + newFileName + "')";
    $.ajax({
        url: docLibraryEndpoint,
        type: "POST",
        binaryStringRequestBody: true,
        data: arrayBuffer,
        timeout: 1000000,
        processData: false,
        state: "Update",
        headers: {
            "Content-Type": "application/octet-stream",
            "accept": "application/json;odata=verbose",
            "X-RequestDigest": jQuery("#__REQUESTDIGEST").val()
        },
        success: function (file) {
            alert("File uploaded succesfully");
            window.frameElement.cancelPopUp(); return false;
        },
        error: function (data) {
            alert('Error: File did not upload Successfully');
        }
    });
});
}
function _arrayBufferToBase64(buffer) {
var binary = ''
var bytes = new Uint8Array(buffer)
var len = bytes.byteLength;
for (var i = 0; i < len; i++) {
    binary += String.fromCharCode(bytes[i])
}
return binary;
}
function getFileBuffer() {
var deferred = jQuery.Deferred();
var reader = new FileReader();
reader.onloadend = function (e) {
    deferred.resolve(e.target.result);
}
reader.onerror = function (e) {
    deferred.reject(e.target.error);
}
reader.readAsArrayBuffer($('#fileInput')[0].files[0]);
console.log('done: ' + reader);
return deferred.promise();
} 

Any help would be greatly appreciated, thank you!

baywet is correct, and your upload method is fine. Alternatively, I like to do this with straight CSOM. You can use FileCreationInformation to upload an attachment

Example library item metadata update with CheckIn / Check Out:

using(ClientContext ctx = new ClientContext(siteUrl)) {
    SecureString passWord = new SecureString();
    foreach(char c in password)
    passWord.AppendChar(c);
    ctx.Credentials = new SharePointOnlineCredentials(username, passWord);

    Web web = ctx.Web;
    List list = web.Lists.GetByTitle(listName);
    var query = CamlQuery.CreateAllItemsQuery();
    var items = list.GetItems(query);
    ctx.Load(items);
    ctx.ExecuteQuery();

    foreach(var item in items) {
        item.File.CheckOut();
        item["Category"] = "My New Category";
        item["Title"] = "My New Title";
        item.Update();
        item.File.CheckIn("Updating Category and Title for list item", CheckinType.OverwriteCheckIn);
        ctx.ExecuteQuery();
    }
}