can i transfer eBooks from laptop to iPad

I'm pretty sure that as long as you use the same account, that you're OK. I know that they allow transferring from the iPod to the iPad. You can always call them to confirm.

That depends on the ebook vendor. Kindle books, for example, can be bought once, and read on lots of devices. Apple iBooks can only be bought on iOS devices. Most of the time it's the account that's important, not the device, but some may have limits to the number of devices registered to the same account, typically 5.

Stanza is one of the best ebook apps you can get, it has iOS and OS X apps. The desktop app will read most every format I've tried it with, and can convert into different formats too, and best of all, sync with the iOS app through iTunes.

Kindle also has desktop and iOS apps, which can sync through iTunes, or the cloud - it even keeps your place in the book across devices. It doesn't support many formats though.

Yes, via Apple's iBook app. See this article: http://support.apple.com/kb/HT4059 "iBooks: Frequently Asked Questions (FAQ)":

Can I download books from other websites?

Yes, you can download ePub files on your Mac or PC. Using iTunes 9.2 or later, add them to your iTunes library choosing File > Add to Library, or drag the ePub file to the Books library on your computer. To read these books, simply sync them to your device.

Cheers!

if it's ebooks from places that use drm to fight piracy then no you need an app made by the ebook manufactor like kindle or barns and noble or other drm ebook sellers

but epub and pdf's without drm can be added to itunes and synced at your leasure