When you start a tournament, what amount of BB's do you start with?
It's a matter of taste, I consider events with 80-150BB starting stacks to be average. More than that is a "deep stack" less than that is a turbo. Now before getting too deep into your time constraints, 30 players in 3.5 hours with rebuys is going to have to be really aggressive. You will be turbo range for starting stacks for sure.
Well let's set the time question aside for now.
If you know you need to accommodate 30 players you just need to determine if you are doing base T25 or base T100 for yourself. There are ways to tailor tournaments to your requirements either way so it's an issue of personal preference.
To accommodate 30 players, my buy recommendation for T25 is a 900 chip set of 240/240/120/240/60 of T25/100/500/1000/5000. This provides 30 starting stacks of 8/8/4/7 plus extras for re-entries and color ups.
I don't have as much experience with base T100 but it seems 10/6/6/1 (of T100/500/1000/5000) for T15K or 10/6/11/1 for T20K are acceptable starting stacks based on other threads. Since you seem game to buy 1000 chips, let's build a set based on the latter
So that's 300/180/360/60 for a total of 900 chips. Definitely helps to have more T1000 chips in play in base T100, that seems to be the trade off with eliminating the T25 chip.
Either of these buys will accommodate starting stacks more than enough for the tournament you are laying out. But not all tournaments you host will be the same, if I say so myself, I think it's good advice to overbuy a little to make sure you cover other types of events you may want. (Deep stack, longer events, etc...)
Now for planning a structure and timing.
So here's the bad news, a 30 player tournament in 3.5 hours is going to have to start really shallow. If you think about it, you will need to eliminate players at the rate of about 8 per hour. (obviously that rate won't be steady, bust outs are slower with the smaller blind levels, but will get much faster with the larger ones.) If you could instead do a 6 hour event, that number falls to 5.
Here's more into how we figure this out.
The widespread PCF rule of thumb is the tournament typically ends when the number of chips in play represents 20 BB. The levers you can adjust to manipulate the length of the tournament are
1) Starting Stack Size
2) Level Duration
3) Rate of level increases.
Personally, I prefer a structure that avoids blinds doubling, I base my structures on repeating 2-4, 3-6, 4-8, 6-12, 8-16 times every denomination in play.
So I would plan these levels:
50-100, 75-150, 100-200, 150-300, (remove T25)
200-400, 300-600, 400-800, 600-1200, 800-1600, (remove T100)
1000-2000, 1500-3000, (remove T500)
2000-4000, 3000-6000, 4000-8000, 6000-12000, 8000-16000.
Now for live tournaments, I recommend a level duration of no less than 18 minutes. This at least means everyone at full table should get to deal at least once per level. If the button is moving slower than the clock, I quickly perceive the play is slow. But you can run your own calculation with shorter levels if that suits you.
So assuming 18 minute levels and the above structure, we are looking at level 12 (18*12 is 216 minutes), where the big blind will be 4000. So to have 20BB in play at that point, we would want there to be 80K in chips in play. Now a 30 player tournament with re-entry, let's just estimate a 33% re-entry rate, or 10 additional stacks. So we need to divide that 80K by 40 entries to get our ideal starting stack to fit in this time. A mere T2000. 20BB to start. Not to mention a short starting stack probably raises the re-entry rate, which would actually mean you tend to run a level or two longer than expected.
If you can allocate 5 hours instead then you can look at level 16 as the probable end. (18*16 is 288 so just a shade under 5h, but you will add in breaks too) The BB here would be 16000, so x20 gives you and ideal T320,000 in play Divide by 40 entries and that boost your ideal starting stack to T8000. That's an 80BB start, that seems doable. If you followed my T25 buy suggestion above, you can cover that because you planned T10K starting stacks. And you can use T10K starting stacks for events when you can allocate even more time, or have fewer players.
You can apply this to your own structure as well.
If you don't have to buy today, take some time to figure out the math for yourself.
1) Plan your structure
2) Decide how many levels you can play in the desired time
3) Find the ideal number of chips in play by multiplying the BB in the "last level" by 20
4) Divide by the anticipated number of entries to get your starting stack. (Feel free to round this to a practical number too, don't need to get overly precise.)
Hope this helps,
Good luck,