Hi Angelos,
Each one of your ccTLDs require their own unique SEO process, as they target different audiences that will search differently (language, seasonality, product/service preferences) and different competitors in each market, that will need a specific keyword research, optimization & link building actions, based on the characteristics and goals that you identify in each one of them.
So, my suggestions to start doing international SEO are:
1. Do a specific keyword & competition research for each one of them. Support yourself with a native speaker (even if it's in English and you also speak English, if it's a research for the UK, then have a British doing the research, as they might search with specific, different terms). Based on this research you will be able to identify your keywords target.
2. Do a technical, content & link audit of each ccTLD. Beyond the typical optimization related elements you will validate, it's important that you compare each of your ccTLDs link profile vs. the ones of your competitors for each country market: What's the gap? What are the link characteristics and volume? What type of links do you need to close the popularity gap? Where do these links to your competitors for each country come from? Based on these data you will be able to establish the necessity and strategy for a link building campaign.
3. Verify how you're ranking with each ccTLD in Google SERPs for each country and the organic search traffic from each country. You mention that you are redirecting the traffic although don't specify how. In general, I wouldn't recommend redirects only in very specific circumstances. To avoid country visibility and traffic misalignment issues what I would recommend is to use hreflang annotations instead.
4. Start tracking and monitoring your results independently in each country market. Most rank trackers support this. You should monitor each independently in Google Search Console, as well as they should have their own Google Analytics to monitor their traffic & conversion behavior per property and country.
So as you can see: Each property focused on a specific country market will require a specific SEO process, analysis and effort.
Check out this checklist: https://moz.com/blog/the-international-seo-checklist as well as post here: https://blog.kissmetrics.com/how-to-international-seo/ to start.
I hope this helps