Why not use the Damphir?
Comparing this to a Tiefling from the DMG
...because the build includes resistance to damage.
Ability Sorce increase: Both +2/+1 with +1 choice between Strength and Dexterity stronger than tieflings Intelligence, both for choice and because Dexterity is one of the strongest abilities, while Intelligence is a dump stat for most classes other than wizard. Stronger
Age: 500 years vs human life span. No aging effects is an added bonus. Stronger
Alignment full freedom vs tendency towards chaos (and weak tendency towards evil), functionally equivalent
Speed: Both walking speed medium, but this adds climbing speed 25 feet. Climbing speed is very powerful, to avoid pit traps, stay out of reach in combat, etc. It is nearly like a permanent spider climb, a level 2 spell. Much stronger
Creature Type: adding undead does not make it stronger or weaker
Damage Resistance is very powerful. A ring of resistance that confers it is a rare magic item with attunement. Necrotic also is not easy to get from resist elements spells. This is comparable to the tieflings Hellish Resistance to fire damage, as fire may be more common
Languages: Common and one free vs Common and Infernal, this is slightly more flexible, but has no bearing on balance
In addition to those, there are the three special abilities, vs only two with the Tiefling
Ancestral Versatility: may be the weakest of them, maybe comparable to the Tiefling's Darkvision with a full skill and tool proficiency.
Blood Sap is quite powerful, providing meaningful healing. In low levels, this can fully heal a character for free. Comparable to 2-6 applications of cure wounds. Compare this with Infernal Legacy which provides a showy cantrip, and later once a day hellish rebuke and darkness (both level 2). I think this is very strong, and stronger, especially in the start
On top of all this you get for free
Lifeblood. Potentially unlimited uses of a 10 feet speed burst. Obviously, compared to nothing, stronger
Overall I feel this is too strong compared to a viable race from the PHB. Most dimensions are stronger than their comparison and one is much stronger. I would essentially always pick this over tiefling, not a good sign.
Comparing to the Damphir lineage in Van Richten's
Ability Sorce increase: Lineages have one score +2, one +1, which is even more flexible. weaker
Age: not mentioned
Alignment full freedom for both
Size: Both Medium, Damphir can choose to be Small, about the same
Speed: Damphir has 35, which is 5 feet faster. You have lifeblood which situationally can add 10 feet speed bursts. I think higher base speed is generally more useful. In addition Damphir gets full speed Spider Climb, from level 3 even on ceilings, which is even more powerful than what you have. weaker
Creature Type: retain detecting as undead vs Humanoid in Damphir. Humanoids are subject to more spells, so being able to chose a non-humanoid type is slightly stronger
Ancestral Versatility: again maybe comparable to the Damphir darkvision. 2 skills is 2/3 of a feat, but darkvision has quite good utility too
Blood Sap matches Damphir Vampiric Bite. The bite also can be used proficiency bonus times and gets advantage when you are bloodied and some other minor tweaks, but deals less damage than a typical weapon attack, and also will heal 2 points less per hit, as it does only d4. Pretty close
Damage Resistance damphir is lacking this, but has no breath instead, which is maybe comparable (diving, no suffocation etc.)
Languages: Common and one free, same
This looks very similar to the Damphir, which has even greater mobilitiy and ability bonus flexibility.
If you are open to suggestions, what you have looks so close, maybe you can just use the Damphir, which is an official lineage instead of adding a very similar hombrew solution. It seems you considered that already however.
The Damphir like your build is a lot stronger than a base class race like Tiefling. Permanent Spider climb is huge. I'll bite my lip about the apparently unavoidable inflation of powerful character build options in spat books. Overall 5e has been pretty good at keeping it in line.