Two Questions.

Yeah, of course you can. All you have to do is get in your car, and drive up slow to the woman. Then honk your horn a few times, and she should come get in the passenger seat of your car. After she gets in, and you two are settled, drive off into some trees, or into an alleyway, or some other area that is usually abandoned. Stop there and wait for a minute, and you should see the car start shaking, letting you know that you two are doing that nasty. She will then take some of your money, get out the car and walk off, so run over her and take it back. I cannot say exactly how big it is, but it is pretty big, just keep playing the game. You never know, maybe you gotta beat the entire game before you can unlock some new areas.

Hope this helps.

Maybe you can pick up hooker I don't know for sure.

I'm the same, I've been playing for about that time, and I'm already onto the 2nd section.

The missions will probably just be harder.
Abd as far as I know, you can't pick up prostitutes.

In GTA IV it's more like RolePlay.

Meaning, in Grand Theft Auto San Andreas, all you had to do was hit the car horn a few times and she would walk over to your car, and ask "do you want a good time".
In GTA IV it's more... RolePlay, in other words more real.

Anyways once he's in the car drive to a secluded place, and of course this time unlike Grand Theft Auto San Andreas, the car doesn't just jump around like it has hydraulics, but you actually, well, see "things". Not recommended if you aren't mature

- Shadow Cast

Yes you can pick up prostitutes it's very detailed to hooker leaps over center console and starts grinding on top of you I was like nooo0o WAYYY once I saw this + thier is other activities the hookers will perfom but it isnt as easy to find the prostitutes as the previous GTa titles and they only are out and about at night look for girls wearing skimpy outfits they useally are working girls and YES evry1 I know to much upon this topic I have issues lolz

Yes you can pick up prostitutes. See top answer for details.
In my opinion, if you want this game to be extra long (which I do), you should try and do alot of side missions. Such as little jacobs drug deliveries etc. Just like myself, most people will be desperate to get on with the game, but if you want GTA to last as long as you waited for it, then try doing alot of side missions. Take time out to get your relationships with friends up as this can prove helpful. Little jacob is good as he will deliver weapons to you (quickly) brucie will even offer a taxi service to you, IN A HELICOPTER!! Very helpful if you ask me.

You can pick up prossies, they are usually "chunky" women wearing skimpy outfits, ive found looking around in bohan near the strip club at night is the best option. There are 3 options, the 20, 50 and 70 dollar options each are, hmmmm.....graphic ;)