i know its a stupid question but can feds command the klingon mirror battlecruiser? it says in the description that "Starfleet and the KDF have obtained several of these vessels and found them fit for frontline duty with minimal modifications". and the second question is, should i spen or save the lobi crystals for later on? will their be more lock boxe events where i can use them?

No, as fed you can't use the kdf mirror battlecruiser.
Well for the lobi, it depends, does the store has stuff you want now? If not, save them, if yes, decide if you want it now or wait and see if better stuff shows up in it.

I'd say you have a month or three to decide.

When news of the lockboxes ending comes time to buy up.

There will be more Lockboxes and new Lobi Store content. I also see specials where say a month in the future you can get the Cadri Box and new Cardassian Lockboxes for those who missed the first round.