Parts you will need to have to hand when refitting are here for the doorv entrance cover
BMW parts Z3 E36 Z3 1.9 Cover, entrance
www.realoem.com
The plastic clips will break when you dismantle it so replacements to hand is handy items 7 and 8 in the list.
For the outer sill cover you will need some replacement hex head screws to replace the rusty ones you take out, items No 4 here
BMW parts Z3 E36 Z3 1.9 Front side panel/Entrance
www.realoem.com
Might be worth considering getting some stainless screws 4,8X16 and some stainless washers to increase the screw hex head when you use these as the heads only have a small flange. Stainless screws on ebay same for the washers
stainless screws here
https://www.ebay.co.uk/itm/181786652459?var=480728974715
Washers here
https://www.ebay.co.uk/itm/313471785352?var=612318782524
When you take the sill covers off also take the plastic jacking points out and clean and treat any rust behind them before replacing them.
Probably best to get the sill clips direct from BMW dealer, ebay items are from Latvia and price is high, use Soper BMW at Lincoln, phone them and order, ask for forum discount and they will post them to you.