SIPP lump sum into bonds before end of tax year

Ealinggold

Hello,

I have read in the pension intro on this site that as an employee I could pay any amount up to my full annual salary into a SIPP.

I understand that there are significant tax benefits, starting a SIPP.
After April the contribution will be capped to max amount of 3,600 UKP, since I will not be working anymore.
Therefore I am considering a quick lump sum payment within this month, before the end of the tax year. Probably my trading volume will be low.

I would like to invest into corporate bonds.

I have a couple of older pension schemes, which I might transfer into a SIPP as well.

Here are my questions:

Which provider is best for purchasing bonds?
Any advice on corporate bonds with good risk/return ratio?
When can I take money out of a SIPP?

I already use an ISA for both cash and self investment.
My tax status is Non Dom (more than 8 years in the UK), and I might start traveling next tax year.

Many thanks in advance