[@Exit] With combat, your best bet if you don't want to develop your ow system is to go off an existing one. Tabletop Books make this a lot easier than one might think. DnD is a good base but if you aren't used to the game mechanics it can be confusing. (And seriously, if you go with a DnD base, do NOT make the mistake I have in the past. Don't let them use ANY version, pick one and stick to it no matter how much players complain. Their complaints are a lot less of a headache than trying to work through multiple versions and homebrews.)  

	Considering you are going classic magic, DnD is probably going to be your best bet for a prebuilt system. 


	If you want to put the time into it just develop your own. For forum, it might actually be the best route. I prefer it actually. (I have  different systems built for many of my own RPs) Thing is, this takes time and a lot of dedication. 

	Yet a base form isn't hard at all. You can start it off easy. Since you want to go classic magic - do a basic spell set up where they create their own. 

	Spell Name: Materials Needed to Cast: Effect/Damage: Draw Back. - Or something along those lines. 
	Then just decide if you what to do the rolls yourself or leave it up to the players to determine if damage is done. (Honestly I recommend handling damage a GM thing. It cuts down on a lot of problems.)
	If you handle it, then come up with a quick system to figure out what hits. Can be as simple as they have a 50/50 chance and flipping a coin to a percentage thing. (Higher the percentage, more damage it does.) All up to you. 

	Just make sure whatever you decide on it fits your personality. If you are anal, dedicated, and will push forward no matter what bomb is dropped on you - a more complex system with less loop holes is probably for you. (And in the ends means you would probably do best developing your own.) If you don't have the time or don't think you can dedicate as much time as you would like, either go Dnd or another Tabletop and run with theirs. (Cut out what you don't want to deal with.)