Hi,
1. No ; All payment plugins are working with HikaMarket.
It just depends what you want to do with them.
And if you're looking for an adaptive payment plugin, there is also MangoPay.
2. Even if you use the plugin in "classical" mode ; you have to provide your payment email account.
For the case where your vendor do not have a (valid) paypal email and if you (your store) sell some product (so, not link to a vendor).
Please note that the "classical" mode can use the vendor paypal account if there is just one single vendor in the cart (and only him).
3. It requires a Paypal application account (which is a subscription to a special service).
Best is to read the documentation (that you mentioned) for that and follow the link in the section:
If you want to create a paypal adaptive application accounts, you can find documentation here:
Paypal adaptive application
.
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.