My RES is already in a 60gal and he’s only 2 years old (he’s more than 5 inches and less than 6 right now). The rule of thumb is 10 gallons per inch. Depending on gender, your final housing should be approx 100 gallons (males) or 125 gallons (females) as females generally grow larger (10-12.5 in.) compared to males (7-10 in.). You generally can’t tell their gender until their carapace is at least 4 inches long though. You should aim for a bigger tank to reduce the amount of upgrades and expenses necessary in their lifetime.

This is the heater I use for my 60gal tank and it works wonderfully: Eheim Jager Aquarium Thermostat Heater https://www.amazon.com/dp/B003M7P9YU/ref=cm_sw_r_cp_api_glc_fabc_Vcc7Fb997TKFY?psc=1

Here is a youtube video I used to build my RES an above-the-tank basking area: https://youtu.be/4KDrUiyAtig

And here are the light bulbs I use: UVA (heating lamp): Zoo Med (2 Pack) Repti Tuff Splashproof Halogen Lamps 75 Watts https://www.amazon.com/dp/B071K95WTD/ref=cm_sw_r_cp_api_glc_fabc_Uic7FbTN48S34

UVB (vitamin D lamp): Zoo Med ReptiSun Compact Fluorescent (5.0 UVB) https://www.amazon.com/dp/B00061V4PI/ref=cm_sw_r_cp_api_glc_fabc_mic7Fb2VJ7PZS

Both bulbs are 10 inches away from the top of their shell when they are basking.