Forget the long john and go with the high waist pants instead- it's easier to breath in.
Go for something in a 5mm and get a nylon outer lining for the type of diving your planning on doing- spearfishing.
You also want an attached hood with no zippers anywhere on the suit. You may want to get a chest loading pad as well for your speargun.
Inner liners are up to you. You have a few options that go something like this:
Opencell- cheapest/ warmest, but hardest to put on. I have this on many of my suits and love it.:inlove
Gold/silver/copper lining- makes sliding the suit on eaiser, but is more expensive and doesn't stick to your skin quite as well as opencell. You'll never know the difference since you've never owned a suit like this before. I also own a couple of suits with theses linings on the inside. Things to know about them: First, the lining wears off over time. Second, they do NOT keep you any warmer than a standard opencell- no "reflective heat" crap works in a wetsuit. They will give you suit a little bit extra tear resisitance, especially if the outside is smoothskin, but they are mainly to make the suit go on easier.
Black Shadow- This is just another spray on coating that ELios puts on the inside of their suit. They call it one of their best glide skin liners that makes the suit much easier to slide on. I have known many people who got this on their suits and loved how much easier they were to slide on. I've never used it before, but oredered it for my new summer monofin wetsuit- my new suit is thin and delicate so I wanted to make sure I wouldn't damage it when putting it on.
Nylon/plush/ super elastic- These are super tough, just like a scuba wetsuit, but no where near as warm as a standard freediving wetsuit. They also are harder to breath in since you loose so much flexibility in the suit due to the extra material lining the inside and out. I wouldn't reccomend them for cold water diving.
No matter which suit you get, aside from the nylon inner lining, you'll want to use some sort of lube to put it on with. I use lube even on my silver and gold lined suits. Lube is a mixture of water and hair conditioner that you can mix up in a spray bottle. Everyone has their own favorite mixture and it pays to experiment on your own. I start out wit a 50/50 mix of each and then just keep adding water to it everytime I use it until it gets to thin to help slide the suit on anymore- then I add more hair conditioner to it.
No matter which one you get your going to love it!:inlove
Jon