Absolutely not a problem firing old ammo provided it is not badly corroded. The white packet with cartridges having the pointed bullet will be Speer/DWM so that ammo will not be that old and the Speer bullet a good one. Speer had an alliance with DWM for some years.

The RWS ammo will be good to go too. Many of the bullets for lower velocity German loaded cartridges used the 'silver' bullets, a nickel plated thin copper jacket. These were often target loads but okay on the thin skinned and light roe deer and small boar.

I use a product available here called "BrassBrite" a sort of liquid cream containing 3.7% w/v hydrochloric acid. Possibly similar to Brasso but more of an instant cleaner with only a little rubbing required for heavily tarnished brass cases. It does a nice job and just polishes off with a clean cloth although I use a damp (not soaking wet) cloth to neutralise any acid residue before polishing off.

If the cases are berdan primed it is better to stay with berdan. Very fiddly to try and convert to boxer although it can be done. I reload berdan primed Kynoch cases for my 404. Made up a pin to fit a spare Lyman decapping rod (22cal I think it is)out of a piece of strong spring steel. Set the case into the shell holder in the press with handle down and case protruding through the top of the press, feel the pin enter one of the twin flash holes and tap out the primer. Knocks out spent factory primers that have been shellaced in no problem.

To convert to boxer primers you need to put the deprimed berdan case upside down over a mandrel after knocking out the original primer, fill the twin flash holes by peening the raised anvil down flat, then bushing the usually larger berdan primer pocket down to the boxer dimension and then drilling a central single flash hole. It used to be possible to purchase thin hollow brass tube that would fit the OD/ID dimensions required for the bushings. I would not apply any heat near the case heads for soldering bushes in. Just make them a good snug fit, after all any primer only seats and seals with a good snug fit. As you can appreciate it is rather involved to convert to boxer primers, hence my preference and recommendation to stay with berdan primers if at all possible. At the end of the day you still have to knock out the berdan primer before you can convert anyway and most sizes of berdan primers are still available.