Another new player recommendations topic

Hello friends,

I am two weeks in and have been looking to optimize my early game F2P time. Currently I am a few days into having my starter Kael at 6 stars.

Legendaries: Aleksandr/Astralon/Longbeard.

Epics: Masoleum Mage/Husk/Reinbeast/Hellgazer/Quargon the Crowned.

Rares: Kael/Athel/almost entirely campaign rares

Asides from Kael I have only leveled up two champs: Warpriest and Warmaiden to 4*, everything else is within their default level range. Currently I have a few questions specifically regarding my progression:

Who to 60 next? Probably the most common question you all see on this board.

Where should my skill books go? Kael got my first batch of rare skill books and I'm saving the rest of the rares for Apothecary or whatever amazing rare that pops up, but I have some epic and legendary skillbooks that I have from campaign rewards and such. A guide by u/wsoul13 extols the virtues of Mausoleum Mage, but that guide is a year old... is he worth dropping my first batch of epic tomes into? Are any of the legendaries I listed above worthy of the lego skill tomes, or do I sit on those for now?

Is there anything specific that I should be working towards at the moment? For instance, should I be attempting to get any and all champion fragments from any available sources? Also, I am sitting on a small amount of blue/purple/yellow shards, is the current event worth opening them on or do I wait for a 2x summon event at all times before opening these? I opened a bunch already during the last 2x event and I want to open what I have now but is it better to wait?

Thank you in advance for any advice and here's to hoping everyone has a happy new year.