You have asked a lot of questions
1st you have to know what your Thread/barrel diameter is. In newer guns there is the standard threads and then there are the WSM threads. Long actions will take short action barrels, but not vise-versa. The head size has to be the same i.e. If you stay in the 30-06 family 280 Rem, 270 Win, 308, 7-08 etc., then any cartridge can be used on a 30-06 with a long action. If it is a short action then you will have to stay with short cartridges like 308, 7-08, 22-250 and 243. Then there is the 222 family. As long as you stick with that head size, you can be OK. 17 Rem, 221FB, 222, 223 and 17FB are some examples. With a Savage you can also change the bolt head to change head size. You could have a 223 and change it to a 308 (both short actions) by changing the barrel and bolt head or vise-versa again. I hope I do not have you confused here. Basically, if you have a long action, you can make it shoot any non WSM cartridge. If you have a short action, you can make is shoot any non WSM cartridge as long as it will fit the short action. As far as special tools, you at least need a barrel nut wrench, no getting around that, unless you do not care if the barrel nut gets chewed up, then you can use a pipe wrench. They cost any where from $25 - $40, depending on where you buy them. I got mine free, there was a special going on at Midway...Buy a A&B barrel and they threw the wrench in for free. An action wrench is a good thing to have, but I think a 5/8" rod turned down and threaded to fit the action screw (I think it is 1/4 - 20) would work, just fine. A piece of bar/flat stock stuck through the ejection port/magazine cut out would probably work too, just be careful about marring the action. A barrel vise is nice too, but a good bench vise with wood blocks would work just fine too. This is not needed, but it sure makes it a lot easier to swap out a barrel. I have all of the special tools, but I also change out Remington barrels and the action wrench and barrel vise works for the Remington's too. You will also need a full length sized case to set head space. I have used go gages and full length sized cartridges to set the head space. Either work OK, but I get a better feel with the steel gages. When I change mine out, I also dab on some no-seize on the threads, to make it easier to change out the next time. Once you have done it once you will be able to change out a barrel in about 30 minutes, ready to shoot. The bolt face, I have not changed, but I am guessing that would take about 15- 20 minutes, once you know what to do. You will find the Savage, the easiest rifle to make a complete change over for the basement gunsmith. If you have any other questions, please send me a PM or post here for others to answer. It almost takes longer to write this response than it does to change out a barrel.