For the first part of your question, most of the information that you want is already available.
Since you wanted an average over the day (or week) the script piped the statistical data for each interval to the Measure-Object cmdlet.
So when we just leave it out that cmdlet you will get all the statistical data not just the average.

In the following script I did just that:

• create a new function, called VM-statavgArray, that leaves out the Measure-Object cmdlet and returns the array with all the statistical data
• added some functionality to write all the statistical data to an individual CSV file for each guest

From there it should be easy to put these values in a graph.
The script only shows the average CPU usage for 1 day.
The data for a week and for the memory statistics can be done in a similar way.

function VM-statavgArray ($vmImpl, $StatStart, $StatFinish, $statId) { 
        $vmImpl | get-stat -stat $statId -intervalmin 120 -maxsamples 360 ` 
        -Start $StatStart -Finish $StatFinish 
} 
#Report for previous day 
$DaysBack = 1 # Number of days to go back 
$DaysPeriod = 1 # Number of days in the interval 
$DayStart = (Get-Date).Date.adddays(- $DaysBack) 
$DayFinish = (Get-Date).Date.adddays(- $DaysBack + $DaysPeriod).addminutes(-1) 

$Report = @() 
get-vm | Sort Name -Descending | % { 
        $vm = Get-View $_.ID 
        $DayCpuUsage = VM-statavgArray $_ $DayStart $DayFinish "cpu.usage.average" 
        if($DayCpuUsage -ne $null){ 
                $report = @() 
                foreach($line in $DayCpuUsage){ 
                        $row = "" | Select Timestamp, Value 
                        $row.Timestamp = $line.Timestamp 
                        $row.Value = $line.Value 
                        $report += $row 
                } 
                $Report | Export-Csv ("C:\" + $vm.Name + "-DayCpuUsage.csv") -noTypeInformation 
        } 
} 

For the second part of your question.
You can get the disk usage statistics with the disk.usage.average metric.
Note that this will return, in KBps, the sum of the data read and written to all of disk instances of the virtual machine.
You can use the similar script logic as in the previous script for this metric.

If you want to see disk IO statistics for individual disks you need to use the disk.read.average and disk.write.average metrics.
But note that you will have to filter on the Instance property to select the disk you want.
Also note that the instances are the disks connected to the ESX server not the virtual disks connected to the virtual machine.
You will need to add the disk.read.average and disk.write.average values together to get the total IO to the individual disk.

function VM-statavgArray ($vmImpl, $StatStart, $StatFinish, $statId) { 
        $vmImpl | get-stat -stat $statId -intervalmin 120 -maxsamples 360 ` 
        -Start $StatStart -Finish $StatFinish 
} 
#Report for previous day 
$DaysBack = 1 # Number of days to go back 
$DaysPeriod = 1 # Number of days in the interval 
$DayStart = (Get-Date).Date.adddays(- $DaysBack) 
$DayFinish = (Get-Date).Date.adddays(- $DaysBack + $DaysPeriod).addminutes(-1) 

$Report = @() 
get-vm | Sort Name -Descending | % { 
        $vm = Get-View $_.ID 
        $DayDiskRead = VM-statavgArray $_ $DayStart $DayFinish "disk.read.average" 
        if($DayDiskRead -ne $null){ 
                $report = @() 
                foreach($line in $DayDiskRead){ 
                        $row = "" | Select Timestamp, Instance, Value 
                        $row.Timestamp = $line.Timestamp 
                        $row.Value = $line.Value
                        $row.Instance = $line.Instance
                        $report += $row 
                } 
                $Report | Export-Csv ("C:\" + $vm.Name + "-DayDiskReadAvg.csv") -noTypeInformation 
        } 
} 

Note that you will need to set the historical interval that corresponds with 120 minutes at least to level 3 to collect these device statistics.