I have a website that is using Cloudflare Pro plan with Argo & Accelerated Gigabyte enabled. I have hosted it on Cloudways on DigitalOcean instant. Do I need a Cache plugin separately for my blog?
May I ask if it’s a WordPress or? I’d try out Cloudflare APO for WordPress, just for testing purpose.
Otherwise, some caching plugin like WP Super Cache could be considered if there’s more than expected web traffic coming to your blog.
Otherwise, I won’t be using a caching plugin alongside the stated features being active and in use withing Cloudflare.
May I ask what is your final goal here? 
Having the best possible, or getting the better results on some Page Speed tool or more related to the end-visitor?