Hello
I've just seen you didn't really get many answers to your question so thought I'd reply.
I filled out the LPA forms (both financial and welfare) for my mother myself. You have to make sure you answer every question or cross out the whole page. Make sure every signature is provided. If your parent has capacity to understand what they're doing, you shouldn't have much problem. You will need a Certificate Provider to sign to say they understand (an old family friend, doctor, such as that).
We filled them out, and got them registered with no problems. If you use a solicitor the fees seem to vary quite a lot for what is really quite straightforward, provided you read it all carefully.
You have to pay to register, I think it was £250 for both of them.
Hope all goes well with it.
R