No experience with the spencers, but the sandies & lacies I'd say 5-6 footer as a starter, then once the little guy starts growing, go with the biggest enclosure you can afford /have room for particularly with the sandies, due to their speed & movement patterns. That said, we have a mature flavirufus in an 8' x3' x4' indoor enclosure who's as happy as. He comes out during the day to bask, has a bit of dig, then basks again until the minute the sun goes down, then it's straight into his burrow until morning. He'd be probably 4' overall length, & while I originally thought he'd need to go into an aviary type setup, his individual habits make him perfectly suited to the enclosure he's in.