Personally, I think there's such a thing as too much gore. But I'm a scaredy-cat, and should probably not be used as a measure for the rest of hte population.
As for your last questions...
1.) You're free to do whatever you like. It's your comic!
2.) Again, you can do whatever you like, but it's an old horror-movie rule that the monster (i.e: that thing that is supposed to scare/unsettle you) is the most scary before you see what it looks like. It's probably scarier/more unsettling to imply what's happening than it is to draw a detailed picture of every internal organ.
3.) If you're going to post your comic on Tapastic, you're going to have to adhere to the Content Policies, which state the following regarding NSFW-material:
Adult Material: Tapastic ALLOWS mature content featuring nudity, non-graphic sex, extreme violence, and strong language as long as it is behind our NSFW filter. Tapastic DOES NOT ALLOW pornography or hateful content that targets a specific person or group of any kind. Any content deemed unsuitable that is not behind our NSFW will be requested to take action. Failure to comply with this request will result in the image being taken down. Repeat offenses will result in the suspension or removal of the user’s account.
So you can post it here, but you have to put it behind an NSFW-filter. There's a button for this when uploading your comic-page - it looks like this:
And if you're drawing the kind of violence/gore that would not appear in a PG-13 rated action movie, you probably should consider putting it behind the filter.