Hi @Minnie_Goldman , welcome to the forum 
You can visit the below link, scroll down to ‘Compare all features’ for a granular comparison of the free Personal plan compared to the paid plans.
As you can see, Custom fields and Rules are available on the paid plans. The will all become locked or unavailable once your free trial period ends.
The minimum seats you need to purchase are two, for Starter or Advanced plans.
If you pay annually you get approx. 2 months free so the minimum cost for Starter, for example, would be USD $263.76 per year, for 2x seats.