Based on my zero experience but more than a little research, here are some suggested plugins that might allow us to meet the user needs. Feel free to evaluate these and/or others, as your experience is vastly greater than mine. The themes I stumbled over while looking for plugins.

In essence, we want a standard conference site build that can be quickly deployed many times over, each then receiving a little design and configuration to meet conference-specific needs.Some conferences will need more help (even with content) than others, so we must cater for all ranges of capability, giving the appropriate level of control to the conference organiser (maybe proportional to their ability).

Plugins

Registration/ticketing

Heart of our solution needs to be a registration and/or ticketing system, flexible enough to cover simple to complex and free paid events. Whatever the plugin, we must make sure that it supports payments the way we (Victoria/NZ) want to do it, but for users all over the word.

Event Espresso 4: Free (Decaf) and paid version (US$70 - US$280). However, I can't see Payment Express (or even Woo Commerce) as integration options.

Events Manager: Also a free and a paid version for US$75 - US$150. However, I can't see Payment Express (or even Woo Commerce) as integration options.

Events Calendar and Events Tickets: Go together. Events Calendar is free and Events Calendar Pro costs US$80-US$300 per year (1 or 10 sites). Event Tickets is free and Events Tickets Plus costs US$80-US$300 per year (1 or 10 sites). Integrates with Woo Commence, which in turn supports Payment Express.

Event Planner: Has a free and paid version costing US$60 - US$300 per year. However, I can't see Payment Express (or even Woo Commerce) as integration options.

Payments

Most conference themes support Woo Commerce, which in turn has many payment plugins, including one for Payment Express. I think this can be configured for credit cards (at least Mastercard and Visa) and bank transfers (good/cheaper, but difficult if attendee's bank isn't in NZ)

Schedule and presenters

Somewhat supported by some registration systems, but we have a real need for multi-strand scheduling, where there are concurrent/parallel sessions.

Timetable and Event Schedule: Free. Looks more polished and better featured than others. Much nicer default views/themes. Should easily handle different sessions. More info on vendor site. US$200 per year for priority support and access to all their themes and plugins

Cr3ative Conference: Free. Vendor site. Might only do single-strand schedules. Looks rough and unpolished.

WP User Frontend: Could allow presenters the ability to manage their own profiles. Free and paid, costing US$50 - US$160 per year

Sponsors

Cr3ative Sponsor: Free. Vendor site. Quite nice presentation of logos/images, than can be hyperlinked. If we will ever need something like this.

Calls for proposals and production of the proceedings

The second most challenging of the requirement areas to meet using Wordpress. Not all conferences need this and those that do often need an advanced and highly configurable system for this.

WP Abstracts: Free and paid versions. Only costs $20/year/site, but vendor looking at bulk licensing option.

EasyChair: Not Wordpress but far more powerful then WP Abstracts. If people really need what it offers, then we can always link to it . Free and paid, with a table of the differences.

Themes

https://themeforest.net/item/eventerra-event-conference-wordpress-theme/15717811?s_rank=14 is compatible with a ticketing sysem https://tickera.com/supported-payment-gateways/ (maybe even included, but no Payment Express support) and payment options like woo commerce. Might only need WP Abstracts and Contact Forms 7 to be ready. Also WPML and Polylang plugin compatible

https://themeforest.net/item/ivent-multipurpose-event-wordpress-theme/13859489?s_rank=30 is compatible with ticketing systems (Events Calendar Pro, Event Ticket Plus, Community Events, Community Tickets) and translation-ready. Older WP versions, and woo commerse.

https://themeforest.net/item/eventum-conference-event-wordpress-theme/12943209?s_rank=1 seems to have most of what Vini needs included, except for payment (via woo or eventsbrite?)

https://colorlib.com/wp/wordpress-themes-for-conference-and-event/

https://webdesign.tutsplus.com/articles/best-wordpress-event-themes--cms-27022

https://themeforest.net/item/the-keynote-conference-event-meeting-wordpress-theme/9718856

https://alienwp.com/wordpress-event-conference-themes/

https://themeforest.net/popular_item/by_category?category=wordpress%2Fentertainment%2Fevents

http://wpconferencetheme.com/

https://athemes.com/collections/best-events-wordpress-themes/

And if I want to keep looking

https://themeforest.net/search?utf8=%E2%9C%93&term=conference+theme&referrer=search&view=list&rating_min=4&platform=WordPress&compatible_with%5B%5D=WooCommerce&compatible_with%5B%5D=WPML

Others

And an interest blog from somebody who pulled together his own conference suite using Wordpress.

Browser not supported