I did the Lester trick on my second playthrough: bought the recommended LCN/BAWSAQ stocks, finished the missions, sold at the spike each character ended up with millions (and it let me buy every property). After that I just collected weekly payouts and did side missions/collectibles to keep the bank healthy. If you want exact stock ticker names for each assassination (Hotel, Multi-Target, Vice, etc.), I can paste that list worked perfectly for me.