A: You can, but I would strongly advice you against it. The opposing party will take advantage of it and will either settle for a lot less than the case is actually worth or deny liability completely. Only experienced PI attorney can properly evaluate your case and make sure you're getting compensated fairly for everything you're entitled to. The attorney will also know how to establish liability (even if there are no independent witnesses) and how to handle litigation process.
Yes, you would have to answer interrogatories and other discovery and without attorney you wouldn't know what information you have to provide and what you can object to which can compromise your case outcome.
A: Unfortunately, your recovery from liability insurance is limited to $25,000. If you have the same limits on your own policy, your insurance won't pay anything on top of it (as they have no exposure). But there could be other applicable policies. For example, if you live with a family member who have separate insurance policy, their policy will cover you.
The experienced personal injury attorney will be able to do a research and find out if there are any additional policies that could be applicable.