Some Advice Please?

Hi, I rerolled 2 days ago for GT and have passed 1000 waves on T1 (game is still in progress).

Since I can farm 1k+waves on T1 I was thinking that a 4th research slot would be worth saving up 1400 immediately for. On the other hand, I also see the benefit of another card slot and some cards. The only "good" card I have is the enemy balance one, the rest are common low tier cards.

I have 4 card slots at the moment and 200 gems. Should I save up the 1400 for the 4th lab slot to increase my research by 25%? Or should I spend 300 on another card slot and pull some cards for it?

Thanks to all who choose to reply.