Time to adjustment will vary from person to person. Just stay seated and relax your legs. When your tendency to coast diminishes, then you can experiment by standing while pedaling, etc. Just stay relaxed. It took me 5 minutes to get used to it, but I took it easy for several days.

Speaking of coaster bikes: My friend went on a vacation with her family and they rented bikes, which were coasters. The husband, being used to freewheel road bikes, stood up and absent-mindedly pedaled backwards, and instantly went over the handlebar and shattered a portion of his front teeth, broke his elbow and shattered his right knee cap. I'd say that, for an experienced regular road-biker, the fixed-gear bike is safer to learn on than a coaster bike.

Good luck. The pub crawl sounds fun.