Perfective and imperfective forms

What about semelfactive verbs - стукнуть, кинуть, сдохнуть, they are not formed using prefixes? There are too many prefixes and verbs differ in perfective/imperfective without adding anything - спрашивать/спросить, взвешивать, взвесить, they may not have a pair or have multiple opposite equivalents. Imperfective may be more common than perfective and vice versa, making them absolutely equal, so that one can't be really explained as "a form" of the other. They exist in pairs.

доде́лать, переде́лать, вы́делать, отде́лать, заде́лать - all add additional senses to делать, not just making them perfective forms but separate verbs, even if these in turn can have additional imperfective forms, e.g. доде́лывать.

Those existing in pairs should be treated like Serbo-Croatian treats them - make the most common one a lemma, and redirect the other one using the templates which I try to keep alive. Treat other variant and secondary stems as alternative forms of one of the infinitives. You notice how usually such pairs don't differ in meaning other than perfectiveness part? :)

Prefixed forms are truly derived words, and have a separate treatment in Serbo-Croatian as well. They add and significantly (almost always unpredictably) modify the original meaning. Each of those prefixes can introduce half a dozen semantic modifications which are listed in grammar books.

There are of course always exceptions and special cases (usually one of the forms shares all of the meanings of another, but has some special ones on its own, which I usually handle by listing them below the redirection template), but the base argument seems to be solid and applicable to the majority of cases.

I cannot agree with you about lemma and derivations. They are not forms, they are separate words. Nouns, adjectives, adverbs are also formed using suffixes and prefixes. This info useful in etymologies, e.g. сделать = с + делать but it doesn't need to be classified as a perfective form of делать, they form a pair. In many cases, the perfective verb is much more common and would be defined as lemma with your criteria (чокнуться) or may not have an imperfective form at all (кануть) or they use suppletive forms - сесть/садиться.