Heathrow connections with separate tickets

When you say "with baggage reclaim" that implies you have to check in again, and hand your baggage in again, for the second flight. What is the minimum check-in time for the second flight? This varies with airline and destination.
The good news, Terminal 2 and 3 are adjacent to each other, no bus or train transfer needed, just a long walk.

• Taxiing, disembark, walk through corridors, IMMIGRATION, pick up bags: 60-90 minutes.
• Change terminals: 30 minutes
• Minimum check-in for second flight, 30 minutes? 60 minutes? 90 minutes?

That adds up to 2½ to 3 hours, with no allowance for your first flight being late. Possible but with very little safety margin. And if you don't check in on time for your second flight, you have no fall-back, you would have to buy a new ticket fro the next flight.

Where and when are you flying from into LHR? Is it a time of year when weather is more likely to have an adverse effect on airport operations?

IF all goes well it may work, but if a bookie were making odds, I suspect you might be in the "snowball in hades" category.

Have you already bought the tickets, or are you still in the shopping process? If the latter, I would build in a longer layover. If the former, I hope you have ice water in your veins, nerves of steel and a cast iron stomach.

I am not saying it cannot be done, but I would not want to try.

If you can avoid checked luggage, your odds of success improve significantly

I'm going there in 8th november with estimated time of arrival at 14:30 and my other flight departure to Helsinki as 18:05. Finnair allow check-ins until 45 minutes before departure. If i have baggage to claim or/and made a connection by my own i necessarily have to pass trough immigration?

If i have baggage to claim or/and made a connection by my own i necessarily have to pass trough immigration?

Yes,
(A) Because the sequence is: disembark - immigration - baggage reclaim - customs - exit.
(B) Because the check in desks, where you hand in your bag again, is in the public area ("landside").

The only way you could avoid immigration is if you had hand baggage only, AND already had your boarding card for the second flight. That way you could stay "airside" and not go through immigration, but you would still have to do an "airside" transfer from T2 to T3.

If your second flight is to Helsinki, I am guessing your first flight is intercontinental. In that case, you have to allow for your first flight being up to 60 minutes late, depending on wind direction on the day.

To make this connection do carey on luggage. The worst part is that you have go through immigration which can be long.

Finnair is a member of the One World Alliance of airlines across the globe. If your initial flight is also a member, say for example British Air or American, when you originally check your bags for your first flight, your bags can be checked all the way through to your final dstination, and you will not need to claim them at LHR.

your bags can be checked all the way through to your final dstination, and you will not need to claim them at LHR.

"Can" being the operative word, not "must" -- if you have purchased separate tickets on One World carriers such as AA, BA or Finnair, they are not required to check through your baggage, or "interline" your baggage. As of June 1, 2016 One World carriers are not required to check your bags through on separate tickets.

I would not count on the generosity of the gate agent (because that's who it comes down to in the end) to have your bags checked through, and fully expect that you would have to clear immigration and claim your checked baggage in LHR if you proceed with this plan.

We did something similar in June of 2016. Planned & booked a trip and then decided to add another destination, so two separate bookings codes. I'm assuming that is what you mean? Both flights were booked through British Air, but the 2nd flight was operated by Aer Lingus. Our seats were towards the door, and we walked hastily to immigration, picked up our luggage, walked through the customs green door, got on the tram to the Aer Lingus terminal, re-checked luggage and went through security, all in under 2 hours. So, not ideal, but sufficient.

In our experience, British Air would give us boarding passes for Aer Lingus flight, but would not interline our luggage.

How did it work out?

Hopefully you made it

Edit... Sure wish OP would let us know what he did and how it turned out, so others could make reasonable plans when in similar circumstances