I always put simple syrup on my cakes and dont have space in my freezer, so can I bake in advance..

Yes, depending on the recipe.  I always bake on Wednesday for Saturday weddings.  Cover them in ganache on Thursday and they'll be fine.

I never used ganache

can i  just frost it without the ganache and let it sit in the fridge till I decorate Thursday and finish it off on Friday?

even when I didn't have an extra fridge or freezer the cakes came first -- i learned not to big grocery shop before i did a cake -- i cleaned out the fridge/freezer -- sometimes tossing stuff that was still good -- but doing that and it stinging is how I learned to have a lean fridge --

your cake will probably be OK but the fridge dries things out while the freezer suspends all the moisture -- you can crumb coat if you want and wrap it like a mummy several times it should be fine

thank you!!

Yes, you can just leave them at room temp well-wrapped and uniced, too. If you'll be working on them Thursday and Friday that's no big deal.

there definitely are cakes that would be fine at room temp for four days but not all of them -- you would want to have tested that in advance and especially if it's a tier cake -- performance is everything -- needs to slice neat and clean as well as hold at room temp after being plated for at least an hour before crusting/staling

best to you