Being engaged to a former bartender, I just take all this stuff for granted! I had to think about it for a moment, but here are your answers:
The bartender will see your group come in, and will most likely put all of you on the same check automatically.
If the bartender is kind of busy, I find it easier and faster to initially ask the group what they want to drink and then relay the list to the bartender. That way if he can't remember one of the drinks, he/she can just ask you.
If the bar is not very busy and people in your group order directly from the bartender, let the bartender know that your group is all on your check, then he/she will know to give the check to you.
As far as the check goes, three things may happen.
1. The bartender may just "run a tab" on your group, periodically asking you or people in your group if they'd like another drink, then give you a check when you ask for it.
2. The bartender may ask you if you want to run a tab, and possibly ask you for a credit card to hold before you order (your credit card won't be charged if you pay with cash at the end).
3. The bartender may give you a cash total after you order the first round of drinks. You can then tell him/her that you'd like to run a tab. If the bartender says no, you are probably at a 3-deep college dive bar--not so good for your business! But if you are in a pay-as-you-go situation, tip a dollar or so per drink after each round. If your tip is a little more on the "or so" side, the bartender might just run a tab from that point.
After you ask for your check, you will get an itemized bill. I recommend that you quickly read over the bill, not necessarily to check for drinks you didn't order, but to see if the bartender gave you anything for free (it will not be on the bill). Sometimes the bartender will do this if he/she had a nice chat with your group. He/she may let you know something like "This round's on me," but not always.
As for tipping, I know there will be some people on this board who do not agree with the following, but if you plan to return to the bar, this is a good guide:
1. If your bartender was friendly and attentive, leave 20% or more (you're writing this off as a business expense, anyway).
2. If your bartender was friendly, attentive, and was also helpful, really funny, did not bug you way too much and/ or gave you a "free" round (more a show of good will), leave 30-35%.
If your bartender gives you your drinks, but doesn't pay attention to you otherwise, leave 15% (unless he/she is leaving your group alone to talk, then leave 20% or so).
I strongly suggest that you try to visit the bar you're taking your clients to ahead of time. Tell the bartender you're thinking of bringing your clients on a certain day, they may tell you about who will be working.
As for non-alcoholic drinks--order a coke or a sprite, club soda with lime, or a non-alcoholic beer (actually has a very trace amount of alcohol, but won't affect you). OJ (orange juice) and club soda is also good. I would not suggest ordering anything like a virgin bloody mary or virgin pina colada in front of your clients.
Hope this helps!