If using W3, do I need other plugins

I’m a bit of a newbie, and have spend quite a few hours trying to figure out which plugins are best for my site. One that I’m using is W3, my questions are:

1.Since W3 incorporates so many aspects of optimizing – including minifying,
I don’t know why I often see posts recommending W3 AND a minifying plugin AND gzip compression And …..etc.
So, could you please tell me if I need any other optimizing plugins if running W3?

2. It looks like you can switch on gzip compression in WordPress itself. Are gzip plugins redundant?

3. I’m using Nextgen Gallery, and their support people basically said Nextgen plays well with everything. But I’ve read reviews that mention conflicts with that program.
When it comes to SEO – as I am an art dealer -I need to know that I’m setting things up so that my images get “spidered.”

3. Or, putting all of the above togetherr, I’d really appreciate a recommendation of an assortment of plugins, for SEO, Cacheing, Google Xmap, Site Security, that work well together, and work with Nextgen.
Thank you,
Sam

https://wordpress.org/plugins/w3-total-cache/