Lambopower is probably not the best place to obtain the answers to your questions. To learn everything about the 924/944/951 and possible motor swaps, join: forums.rennlist.com (click on watercooled + turbo links). Every question you have has already been answered.
for starters...
1. Don't use the 924 chassis for a motor swap.
2. A 944/951 is a much better platform. LS1 engines are being placed into them.
3. Price wise... your looking at a minimum of 10k-15k for an engine swap if you DIY.
4. A lot of great 944 turbos on the market right now at amazing prices.