Thinking about getting ~350 .25 chips
That is excessive. Even at a full ring table of 9 players that is 38 chips each. Even in the softest of games, no reason anyone would need more than a barrel ( 20 ) of fracs. Making change is very easy and personally would recommend getting in the habit of doing so instead of planning on everyone having the the correct chips to bet/call with.
150-200 $1 and ~50 $5 chips
That is pretty good but would say 200 X $1, 150 X $5 and at least a barrel of high denoms ( $20 or $25 ).
.50 chips be worth looking into?
A .50 chip in a .25/.50 cash game is a bad idea. It serves no purpose that the .25 can't cover. Denom jumps should always be in the 4-5x range.
Buy ins are typically 30-50, but can go up to 100 per person.
Let's says it's a crazy night and assume a full table and everyone max buy-in. You are looking at a $900 initial investment plus any additional addons.
If you went with your original plan, that is only a bank of $537.50 with your 600 chips.
350 x .25c
200 x $1
50 x $5
If you adjust to the below, you end up with the same number of chips but now have $2k in chips.
200 x .25c
200 X $1
150 x $5
50 X $20
With this breakdown, I would recommend 20 x .25c and 20 x $1 for the first $25 of the buy-in then anything in addition would be paid in $5s.
So players 1 buys in for $30 as below.
20 x .25c
20 x $1
1 x $5
But player 2 buys in for $100 and would be given the below.
20 x .25c
20 x $1
15 x $5
And finally, if this truly is a limp-fest, you might want to try moving down to .05/.10 or .10/.20.