Would an SSD speed up a slow Laptop

[ppppenguin]

Well done. It's usually easier to instal from USB stick than DVD. Optical drives can wear out - most are pretty old now - or get muck inside. DVDs can get damaged - if you try to write on the label side with a ball point pen you can cause massive data loss.

I use Mint Cinnamon so the look and feel will be somewhat different to Mint Mate. Most things should just work. Web browsing, documents and spreadsheets, photos and videos are all handled with pre-installed applications. But you don't have to use them if you don't like them. If you don't like (for example) the PDF reader you can browse for others using the Software Manager which should be easily accessible from the "start" button. Libreoffice will save documents as .ODT (open document text) files by default. It can open and save .DOC and .DOCX files but I recommend that you only use these when you have to work with other people who only have Microsoft Office. Repeated conversion between DOCX and ODT can occasionally give problems. Compatibility isn't perfect but it's good enough for most purposes.

You don't really need anti-virus programs with Linux. One thing I recommend is installing Ghostery as an add-on to Firefox. Look in Tools>Addons. It makes the web much pleasanter to use. Mike Watterson will probably recommend Noscript but that needs some work for best results.