Is it okay to place a tv and computer against a wall with baseboard heat? I like the plain lower tv stands without a back, but wondering if that is okay against the baseboard heat?

Not a good idea.

Should I use a back panel to protect the tv?

I doubt it would help.

What about a desk with computer? Will the heat harm the computer?

Not a good idea.

If I went with one of those huge entertainment centers with bookcases would they interfere with the heater's ability to heat the room?

Yes, it will interfere with the distribution of heat.

The bottom line is that you want to keep heat sources open so the heat can circulate and you want to avoid having electronics near heat sources.

If you can close the vent and very little heat comes out of it, it would probably be okay. If not, then I wouldn't do it.