should I buy flo's or any wheel

No. 

There are tons of threads that will order the bang-for-the-buck cycling gear improvements, and wheels are about 5th on the list...behind a decent riding position with aerobars, aero helmet, miscellaneous cleanup (tri suit, cabling, getting rid of the aerodrink straw), and a decent trisuit. Shoecovers even rate higher than getting a rear disc.

Most people buy wheels because they look cool. You'll have to decide whether that's your criteria, and when to get them. They work, they're just far down the list. As a previous poster stated, your biggest gains will be getting on a tri bike with aerobars, and getting into a decent aero position. Everything after that will be a rounding error. 

They're usually pretty crappy. I think Felt's come with some nice, deep AL wheels: The TTR#'s. I'm spending a good amount more for my incoming SHIV Pro, and the wheels on those are going to be sold the instant I take delivery.

I would get whichever one fancies you the most. I got wheels first since I can use 'em on my road bike, and I wanted to delay the tri bike purchase ever so slightly to see what would be available. Lo and behold, the new SHIV's came out during the time I bought the wheels. Whatever makes you happy and will make you want to go faster, do that.

There are a number of factors that affect your triathlon bike speed.  IMHO this is how I would rank them in order of importance:

1. Powerful rider (i.e. good sustained power or watts-to-kg on hilly courses)

2. Proper aerodynamic position (i.e. TT/Triathlon position: aerobars with a steep seat angle)

3. Skin tight clothing (i.e. Skinsuit or a snug tri top/shorts)

4. Aerodynamic bike (i.e. aero frame tubing, clean cabling, cleanly placed or no bottles and bags)

5. Aero helmet vs. regular vented helmet

6. Aero Wheels vs. regular wheels 

7. Race tires vs. regular tires (low tire Crr)

8. Latex Tubes vs. Butyl Rubber Tubes

In terms of value-for-money a wheelset does not give you a good bang-for-the-buck.   In my humble opinion a race wheelset is one of the last upgrades a triathlete should be making.

Bikes 2-4 times that amount will still come with lesser quality wheels. These will be used for training. One reason this is done is that people will want to select their own race wheels anyway. Hopefully you saw some of the other responses and are less focused on the wheels.

where can you rent race wheels???

I'd be interested in that...

bingo (IMO)

most LBS rent them out or you can try here

racedaywheels.com