In my opinion, the litterature on this topic is very scarce and hugely important. I never know how much to raise. I play regularly 2-5 NLH and pretty regularly against the same players. Usually, the players are pretty loose. I am on the button with AJ of spades after 7 people limp! How much do you raise there? I tend to follow Slansky and his 4 times + one every limper rule and his idea of big pot hands vs small pot hands. Here, of course, that would mean raising to 50, which is silly. I am very familiar with SPR which suggests perhaps only calling here. I made it 35$.

This is so table and villian dependent it is really hard to easily address. I played a 2/5 Sat night where a 50 open would get 3-4 callers. 3! 3-4 times raise would get multiple callers. I have also been at 2/5 tables where 25 gets you HU or 3way. Things to take into consideration when sizing a raise are:

stack sizes of most likely to enter pot
how villians play (tag vs lag vs calling stations ec)
hero's image and activity over last orbit or 2
hand strength - multistreet hand plan
table standard

Why?

It might be, it might not be depending on the limpers

a) limp calling range
b) limp folding range
c) stack sizes
d) post flop play
e) chances you get limp raised or 3 bet from the button etc

Basically, you are thinking about the game way, looking for answers that don't exist. Think about specific situation and what you want your bet to achieve, not pointless generalisations.

There is no answer to your question.

Took the words right out of my mouth.

35 is WAAAAY too low here. You are going to get called by too many opponents.

You need to make it 60-70ish if you raise. If you aren't willing to commit that much pre because you think a few of your opponents are going to call and you aren't comfortable playing this 3-4 ways then limp in and stack them when you hit a big hand.

I really think that it would benefit you greatly to expound on your own thoughts further here. You mention:
1. the literature being scarce
2. not knowing how much to raise yourself
3. knowledge of Sklansky's reccomendation

Then you conclude that Sklansky's reccomendation is "silly" without any rationale for why you believe this. You also didn't list any supporting reasons for the bet size that you chose.

I'm not saying that Sklansky is a diety or anything, but he supports his ideas quite thoroughly in his writing. If you read his ideas, you may reach a different conclusion, through careful examinations of his reasoning. It's entirely possible that the game is slightly different than when he wrote his books, and that tweaks are necessary. However, I would consider it unwise to dismiss his ideas just because the number of dollars to bet seems "silly" on first glance, without any analysis.

Reading this, I was reminded me of this dilbert.

This

And this.

Basically, things like 3bb+1bb for every limper is just a general template. There are tons of other considerations (elucidated well by the quoted posts above ^) that go into deciding sizing. You have to use your discretion/reads/skill to determine these things at the table. Sometimes this will even just mean trying out certain sizings at different times.