'98/'99 boxster

[78F350]

Add a low temp thermostat as well? Yes.

Brakes - check of course, any reason to upgrade? No.

I've read about deep sump kits for oil - good idea to add as well? For a street car? No significant benefit. On the track with track tires, Yes.

And talking of oil, should I attempt to keep the same as was being run or switch to (Mobil 1 - what)? We love "what is the best oil" threads! Go ahead start a new one. or search and read the gazillion posts that we already have on the subject.

Lastly, anything specific on suspension? You can probably learn a lot from the posts that came up from "Speedyspaghetti" trying to sort out his wobbly steering and vibration: 986 Forum - for Porsche Boxster & Cayman Owners - Search Results

Rear trailing arms ( aka track arm, rear control arm...) often start to rattle over small bumps when they wear out. Pretty simple to replace and cost roughly $200 each. Install new rear control arms

On two of about twelve 986s I've bought the rear suspension brackets were cracked by the toe adjustment. I think it's more common on the earlier cars, 97-99 and was reinforced in later years. Replacing the rear suspension bracket