The order which you purchase your items is up to you. If you want you can run right for Perseverence, or get it after Boots and a Bracer or two. I favor getting a Ring of Health as early as possible, then getting Boots and some Stat items, then finishing up my early game shiz with a Void Stone. Perseverence is great for running around the map ganking and for staying in your lane. It's just lovely for Sven.

I would recommend waiting for Storm Bolt to be maxed before roaming the map for kills. At level 7 you should have just enough mana to use Storm Bolt three times, which means you can go as far as killing a wimpy hero online gold all by yourself (although you should never waste mana like this). Remember that Sven has the ability to tower-dive early because of his beefiness. You can run right through the first level tower to get off a second Storm Bolt if your gank gets a bit botched.

Hopefully you can finish up Boots of Travel at a reasonable time. The sooner you get it the sooner your ability to gank skyrockets. Teleport to a lane and run down your unsuspecting target, turn on God's Strength in one lane, finish a tower, Teleport to another lane and slaughter a hero with GS still going, etc. Your added speed lets you keep up and throw off that finishing Storm Bolt with far greater ease. Keeping up so you can hit more with GS on is an easier task because of Boots of Travel.

Again, large battles are basically an exercise in luck and the element of surprise as far as using GS goes. You might get disabled immediately or you might kill two heroes before anyone even realizes what happens. Always cast GS where people can't see you and the latter situation will be most likely to happen. You have 25 seconds, that's a long time!

Linken's won't exactly dramatically alter your game but it's a nice asset when it's completed. You shouldn't have mana issues ever again which means more Storm Bolts! The Spell Block may save you from an ugly Cyclone which is an infinitely awesome thing when it happens. Even if you're saved from Hex that's three more seconds of rampaging with God's Strength on (or off).

Radiance is, as said, the typical tank's damage item. For Sven it means you don't need God's Strength on all the time to deal physical damage. Sven's late game isn't terrible but a lot of heroes (mostly ranged ones) have a much easier time carrying than he does. Try to end the game as soon as possible if you don't have an ally who's stomping ass. Use God's Strength to siege and if things go well the enemy base tower will go down with ease.