IC Cards or single tickets? Reserve Shinkansen ticket or buy online?

I feel kinda stupid to ask but, i'm easily overwhelmed with choices and anxiety, that i screw up, so i need help. More i'm searching for places to visit, its harder to decide what to do. I already dropped visiting Shizuoka and Nagano

I have 20-day trip to Japan at the end of February/ beginning of March.

The itinerary is far from finished, but this is closest to what i planned:

Day 1 (morning arrival) – Day 6 – I would wish to visit Kobe and Himeji, but i don't know if day for each or day for both. Osaka and Kyoto i take as a must.

Day 7 – either chill day Kyoto/Nara or go to Sekigahara and then to Nagoya and move to Tokyo and Chiba

Day 8 (Friday) – starts event in Chiba, which is the main reason to my Japan trip. I would either already be there or take morning Shinkansen to Tokio and then move to Chiba

Day 9 – Day 11 – Event and maybe day or two in Chiba area (maybe Tokio visit)

Day 12 – either still in Chiba or move to Fuji (town), leaving luggage in Yokohama/Kawasaki

Day 13 – Day 16 (or 17) – From Fuji town visit Shiraito Falls and then through western side of mountain travel with train to Kofu/Fuefuki/Yamanashi and staying there – some hiking and onsen

Day 17 (or 18) – Day 20 (late night departure) – travel to Hachioji and then to Yokohama/Kawasaki and stay there till the end of the trip.

I kinda thought about streamlining it and just be in Osaka/Kyoto, Chiba for event and Yokohama till departure and be done with it. And while there are so many other places around i didn't see yet in the area, i kinda want to visit different places (and more nature/old structures) while not traveling too far away. Also don't know when i will be able to go back again.

I expect for Chiba and Yokohama, getting SUICA is better, but i'm not sure for rest of the trip. I know in Osaka is better ICOCA, but i heard my brother had some trouble with it in Sekigahara.

With Shinkansen i still don't know specific day, but i want make sure if i should reserve as soon it will be possible online through website or just buy ticket at station day or two before leaving. Are Fridays more full like in other countries? (Basically i would either travel on Thursday evening from Nagoya or Friday early morning from Osaka)

by Boring-LoserNo1