Hi,
1) There are options in HikaMarket which allow you to deactivate the front-end management, deactivate the vendor registration, hide the vendor links, etc.
So you can deactivate main features if you want.
2) We are currently working on "Paypal Adaptive" which is a special paypal service. With this plugin the money will be automatically send to several "receivers" at the same time (you and the affected vendors).
The current way in HikaMarket is to create invoices in the backend. We will publish a plugin which will create invoices thanks to a cron-task but the payment is still manual.
3) Yes, the "multi-vendor" have all features of the "front-end".
You can see it in the comparaison page:
www.hikashop.com/en/hikashop.html#hikamarket
At least, the "front-end" version is a light version of the multi-vendor, with just one single vendor (your store).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.