First Go to Installing Ubuntu Alongside a Pre-Installed Windows with UEFI and read everything very carefully. Even though the answers are for dualboot, you can choose to wipe Windows and replace it with Ubuntu at the time of installation.
To answer your questions...
1) Will I be able to install Ubuntu 14.04 LTS on my new Acer Aspire ES1-512 C32A laptop, which is a 64 bit OS, has 8GB RAM (upgraded it) and a 500GB HDD (7200rpm). Boot mode is set to: UEFI?
This is hard to say as computer manufacturers often use different internal components for different batches of the computer with same model number. The best thing to do is to boot from the Live USB you created and select "Try Ubuntu without installing". This option will not make any changes to your computer and you will be able to check if everything works or not.
2) I have created a USB Flash drive install of Ubuntu using Universal Installer app - I believe it worked, even though it was stuck on 99% but when I pressed "Close" after 15 mins, it came back saying installation completed successfully - can I assumed this worked or can people suggest another installer ISO app?
Try the Live USB without installing as mentioned above. If it does not work, try creating the Live USB again.
3) When I restart my laptop and press the F2 key to enter BIOS mode, I switch over to Boot section and I am presented with Boot Mode of UEFI and then the option set boot sequence of drives, which would be my USB drive. My question is, what should the Boot Mode be when I go to change the boot order sequence - should it be UEFI or Legacy?
For a system that just boots Ubuntu, it does not matter if you choose UEFI or Legacy. The installation program will use the appropriate process. If you intend to use UEFI, at the time you choose the Boot drive, make sure you choose the USB with UEFI.
4) If/when I eventually wipe Windows 8.1 and replace with Ubuntu, is there any special I need to do from my end?
If you select the option to replace Windows with Ubuntu during installation, it will erase everything in your hard drive including other partitions such as
D:\. If you have data, music, photos, etc. in another partition, copy them in an external drive before you start. You may also choose "Something Else..." and manually select the partitions for Ubuntu. This requires some knowledge of the partition scheme used by Ubuntu.
5)Will things like Wireless LAN | SD Card Reader| Touchpad work straight off the bat or do I need to install specific drivers?
Most things should work. Ubuntu has most drivers already built in. The two exceptions are graphics cards and WiFi cards. Even for these opensource drivers are built-in. If your WiFi card needs a proprietary driver, you connect your computer by Ethernet during installation and check the appropriate box to install these additional drivers at the install time. This can be also done later by running the appropriate program that looks for and installs additional drivers if they are needed.
Hope this helps