1.) Eh. It's not that great on its own. To be honest, I love the one Energy for 40, but Pokemon like Luxray GL LV.X can do it for 60. Ruthless Tail is a decent attack, but kind of expensive. Nonetheless, a nice back-up attacker to have.
2.) The Body is what really makes this card shine. Continuously healing your damaged Pokemon will ensure that bulky Pokemon such as Tyranitar Prime stay alive as long as possible. Mother Gengar utilized Nidoqueen pretty well, also.
3.) Combos? Well, just tech a 2-1-2 line in any deck that has tons of HP. Flygon can take hits while healing, and Gengar, as mentioned before, used Nidoqueen as healing support.
4.) Definitely a 4/5. This card's potential has seen lots of play, and will continue to do so throughout the format.
5. I think it's alright. Nothing too special.