Either the shard or the collar is fine. Might as well just use the one you have though.
for tier 5, and are good to have. at tier 6, you can combine them in the genetech lab to make which will be useful until tier 8 or so. you should pick up because blasting can help out a lot. maybe something like since it scales by tier and it's nice to have two attackers that heal.
for scrolls, probably as an infinite use healer. 10% heal every round is pretty good. if you want something higher end, is very good, offense, defense, and healing. it's the cheapest scroll of its kind, but still kinda pricy. perilous whirlpools are always nice for extra freeze chances, and you have two of those. cobalt eternal scrolls and sancturia exodin scrolls are nice for some defense, along with fatal fire scrolls. it's hard to really suggest other scrolls because most of the good ones come from challenger drops or plots, making them expensive and/or hard to find.
Like kbbob said the freezewand/reborn wand + Knocker will be your best weapons for a couple tiers.
I would probably add in Divine Denizen to the scrolls that I would say to give a shot.
As for which freezer to use, it is really such a marginal difference, it probably doesn't matter at all which freezer you use at this point. Whatever is cheapest is fine (probably Gorgun?)
[Center] [tp=thesovereign] :dmg🔥 [tot=thesovereign] :dmg🔥 [egg=thesovereign] [spoiler=Interesting High Score Tables][url=https://subeta.net/games/battle/scores.php?enemy=206]Paramesian Buttwing Bomber[/URL] [url=https://subeta.net/games/battle/scores.php?enemy=210]Paramesian Recycle Beast[/URL] [/Spoiler][/Center]