Buyer Rapport with Sellers Broker

I am trying to understand what a reasonable relationship looks like between a buyer and the sellers broker. I've been working towards an LOI on specific deal. This is as far as I've gotten on any deal. So far, I've only communicated with the sellers broker via email. Submitted NDA. Gotten initial CIM. Many questions outstanding. Haven't spoken with them real-time. Is this the normal professional procedure? Should the broker be initiating this when they think the time is right? If they're not, is this a sign they a) don't think I'm a legitimate buyer or b) they're skeptical that the seller's expectations represent a deal that can close? Should I be setting up a call to build a rapport with the seller's broker? If so, at what stage? Would be interested in seller's broker perspectives in particular. Thank you.