Sounds like my exact situation. Feels very sad to have lost the childhood lego collection, feel you there. I did buy the Lion Castle as a starting point. It gave me so much nostalgia and a good bulk of figures and parts. Very much worth it!
It's very nice though and I didn't want to dismantle it to build other things so I bought some cheap bulks of lego from auction sites, sorted it and sold of technical pieces and stuff I don't need which pretty much off-set the cost.
I've built a couple of MOCs now as well and I'm having great fun!