Cast Iron Steam Boiler not drained in 30 years

My lower New York zone 6a well insulated basement is 2800sqft. There are 4 well-insulated windows and two wide insulated doors, Most of the basement is underground. The temperature ranges from 60 to 65 degrees during the winter. Even during the rare -15 spell the temperature never dropped below 50 degrees, and quickly returned to 60 degrees afterwards. I have been using the basement for storage, gym and work area and never really had an issue with the temperature. Plus the basement is dry and comfortable. Lately I have been thinking of making a space for the kids to be safe and hangout on those rainy/windy/snowy days. I think I should put in a two zones of baseboard hot water heat to take the chill out of the air. This should be easy because the furnace is right there, and for the most part I only have to pipe the returns. My math is probably wrong but my idea would be to put in 20' of baseboard on either side of the basement. Is this enough to raise the temperature 5 to 10 degrees? Thank you for any suggestions and/or advice.

I have a Weil McLain boiler that had a new 3/4 " relief valve put in.....then a month later I had to turn my home's Main Water Supply off and on twice due to a shower repair issue (there is no shut off valve for the shower). Each time I restored Main Water to the house I felt a sudden powerful burst of water rush back into my home's system. Now my McLain Weil boiler has a slow drip again....one month after it was repaired! So annoying! It only drips when the system is actively heating. I have a long container under the pipe that is more than enough to collect the dripping. I empty it once every 24 hours and I am ok. Yet, why couldn't a new relief valve sustain the restoration of the Main Water Valve? I have a straight handle that I move from the 12 o clock position to the 3 o clock position for off and then reverse the process to put it back on again. The lever has some resistance, so when I restored it I just went from off to on all at once. 1 and a half seconds. IF I had forced myself to move the lever slowly/gradually...would that have made any difference? This happened 12 years ago too. Yet that time the relief valve wasn't new so I paid it and shrugged it off. In the future I'm gonna eventually need to turn off my home's main water. I don't want it to always result in causing my boiler (working fine at that moment) to start leaking. Please share any thoughts everyone. Thanks! Steve