You do not have to re-delegate. Simply transfer the additional tez to the address. The new tokens are subject to the same waiting period as before. You will continue to earn rewards on the initial 100 XTZ, and after 7 cycles, you will start earning rewards on 250 XTZ.
First you have to find out the snapshot# with RPC:
snapshotnum = chains/main/head/context/raw/json/cycle/CYCLE#>/roll_snapshot
Then you get the level that snapshot was. heres how its done in python, showing the constants that are used:
snapshotlevel = ((<CYCLE> - constants['preserved_cycles'] - 2) * constants['blocks_per_cycle']) + ((int(...
It takes a minimum of 8K Tez (*not tezzies) to start self-baking. You will also need a fair amount of linux command-line experience, as there is no GUI. There is the 3rd party toolset, Kiln, but it is still command-line setup (Kiln also requires additional CPU/RAM).
Your computer running the node and baking software only needs 2 CPUs (virtual or cores) and ...