danilob, the Seafoam fuel additive gets mixed reports and reviews and I am not sure why you would need it after using fuel cleaners before and having injector spray patterns perfect now btter whilst you are carrying out the other cleaning to put in two or three tankfuls of petrols with greater cleaning additive packages (like Shell V-Power as an example) .
You did not mention air filter(s) engine (cabin) but given the other work I assume you have renewed them.
I am not sure the Seafoam intake spray will achieve much but if you want to give it a go and I could well be wrong.
For the engine oil if it is sludge'd up and dirty then you may want to consider using an engine flush before this oil change, then using the Castrol GTX Ultraclean until your next oil & filter change when you could consider a better oil. Just one example of an engine flush. - https://www.millersoils-shop.co.uk/engine-flush
Note if you use a Haynes manual they usually have some errors and omissions in them, as with all information you get from any source including me!) cross check against one, two, three, other (reliable) sources.
If you use an engine flush follow the instructions for that then for the oil change as well as the usual instructions -
for all jobs allow loads more time that you think it will take, never be in a rush
if this is the first time you’ve done an oil change on this car have the loan of an oil filter removing tool
have the existing engine oil as warm as possible before draining to be able to get as much existing oil and muck out as possible
remove the oil filler cap as this will allow the oil to drain better
protect yourself from hot oil when draining
leave oil to drain for as long as possible to get as much existing oil and muck out as possible
towards the end of the drain pour some warm(ed) fresh oil in to act as a final flush and allow to fully drain
* - make sure you have the oil filter seal on the old filter or off from the filter housing on the engine - *
clean sump plug and drain hole and filter housing opening
before fitting the filter smear clean oil around the seal of the oil filter and fit filter hand tight then as instructions – do not over tighten
replace sump plug (and new washer?)
steadily refill oil, start with about two thirds of the stated quantity of oil (as refills never take the dry fill quantity stated), leave to settle for a while, top up very slowly, better to need to add more than overfill, leave to settle before checking again, continue until it is near the maximum mark on the dipstick
start the engine and check for leaks (after your first drive check for leaks again)
then, if you want to or it is appropriate, top up to maximum as per instructions.
I hope this also helps, good luck let us know how you get on.